The growing threat of NDM-producing E. coli with penicillin-binding protein 3 mutations in the United States - is there a potential role for durlobactam?

We report identification of 5 patients with infections caused by NDM-5-producing E. coli harboring PBP3 mutations that showed reduced susceptibility to aztreonam-avibactam and cefiderocol. Durlobactam, a novel diazabicyclooctane β-lactamase inhibitor, demonstrated minimum inhibitory concentrations ranging from 0.5 to 2 µg/mL supporting future investigations into a potential role in clinical management.

Real-world evaluation of imipenem/cilastatin/relebactam across US medical centres

We assessed 160 patients who received imipenem/cilastatin/relebactam for ≥2 days. At treatment initiation, the median Charlson Comorbidity Index was 5, 45% were in the intensive care unit, and 19% required vasopressor support. The in-hospital mortality rate was 24%. These data advance our understanding of real-world indications and outcomes of imipenem/cilastatin/relebactam use.

Development of Predictive Models to Inform a Novel Risk Categorization Framework for Antibiotic Resistance in E. coli-Causing Uncomplicated Urinary Tract Infection

BACKGROUND

In clinical practice, challenges in identifying patients with uncomplicated urinary tract infections (uUTIs) at risk of antibiotic non-susceptibility may lead to inappropriate prescribing and contribute to antibiotic resistance. We developed predictive models to quantify risk of non-susceptibility to four commonly prescribed antibiotic classes for uUTI, identify predictors of non-susceptibility to each class, and construct a corresponding risk categorization framework for non-susceptibility.

METHODS

Eligible females aged ≥12 years with E. coli-caused uUTI were identified from Optum's de-identified Electronic Health Record dataset (10/1/2015‒2/29/2020). Four predictive models were developed to predict non-susceptibility to each antibiotic class and a risk categorization framework was developed to classify patients' isolates as low, moderate, and high risk of non-susceptibility to each antibiotic class.

RESULTS

Predictive models were developed among 87487 patients. Key predictors of having a non-susceptible isolate to ≥3 antibiotic classes included number of previous UTI episodes, prior β-lactam non-susceptibility, prior fluoroquinolone treatment, census bureau region, and race. The risk categorization framework classified 8.1%, 14.4%, 17.4%, and 6.3% of patients as having isolates at high risk of non-susceptibility to nitrofurantoin, trimethoprim-sulfamethoxazole, β-lactams, and fluoroquinolones, respectively. Across classes, the proportion of patients categorized as having high-risk isolates was 3-12 folds higher among patients with non-susceptible isolates versus susceptible isolates.

CONCLUSIONS

Our predictive models highlight factors that increase risk of non-susceptibility to antibiotics for uUTIs, while the risk categorization framework contextualizes risk of non-susceptibility to these treatments. Our findings provide valuable insight to clinicians treating uUTIs and may help inform empiric prescribing in this population.

Differential in vitro susceptibility to ampicillin/ceftriaxone combination therapy among Enterococcus faecalis infective endocarditis clinical isolates

OBJECTIVES

To investigate the genomic diversity and β-lactam susceptibilities of Enterococcus faecalis collected from patients with infective endocarditis (IE).

METHODS

We collected 60 contemporary E. faecalis isolates from definite or probable IE cases identified between 2018 and 2021 at the University of Pittsburgh Medical Center. We used whole-genome sequencing to study bacterial genomic diversity and employed antibiotic checkerboard assays and a one-compartment pharmacokinetic-pharmacodynamic (PK/PD) model to investigate bacterial susceptibility to ampicillin and ceftriaxone both alone and in combination.

RESULTS

Genetically diverse E. faecalis were collected, however, isolates belonging to two STs, ST6 and ST179, were collected from 21/60 (35%) IE patients. All ST6 isolates encoded a previously described mutation upstream of penicillin-binding protein 4 (pbp4) that is associated with pbp4 overexpression. ST6 isolates had higher ceftriaxone MICs and higher fractional inhibitory concentration index values for ampicillin and ceftriaxone (AC) compared to other isolates, suggesting diminished in vitro AC synergy against this lineage. Introduction of the pbp4 upstream mutation found among ST6 isolates caused increased ceftriaxone resistance in a laboratory E. faecalis isolate. PK/PD testing showed that a representative ST6 isolate exhibited attenuated efficacy of AC combination therapy at humanized antibiotic exposures.

CONCLUSIONS

We find evidence for diminished in vitro AC activity among a subset of E. faecalis IE isolates with increased pbp4 expression. These findings suggest that alternate antibiotic combinations against diverse contemporary E. faecalis IE isolates should be evaluated.

Bacteriophage and antibiotic combination therapy for recurrent Enterococcus faecium bacteremia

Enterococcus faecium is a member of the human gastrointestinal (GI) microbiota but can also cause invasive infections, especially in immunocompromised hosts. Enterococci display intrinsic resistance to many antibiotics, and most clinical E. faecium isolates have acquired vancomycin resistance, leaving clinicians with a limited repertoire of effective antibiotics. As such, vancomycin-resistant E. faecium (VREfm) has become an increasingly difficult to treat nosocomial pathogen that is often associated with treatment failure and recurrent infections. We followed a patient with recurrent E. faecium bloodstream infections (BSIs) of increasing severity, which ultimately became unresponsive to antibiotic combination therapy over the course of 7 years. Whole-genome sequencing (WGS) showed that the patient was colonized with closely related E. faecium strains for at least 2 years and that invasive isolates likely emerged from a large E. faecium population in the patient's gastrointestinal (GI) tract. The addition of bacteriophage (phage) therapy to the patient's antimicrobial regimen was associated with several months of clinical improvement and reduced intestinal burden of VRE and E. faecium. In vitro analysis showed that antibiotic and phage combination therapy improved bacterial growth suppression compared to therapy with either alone. Eventual E. faecium BSI recurrence was not associated with the development of antibiotic or phage resistance in post-treatment isolates. However, an anti-phage-neutralizing antibody response occurred that coincided with an increased relative abundance of VRE in the GI tract, both of which may have contributed to clinical failure. Taken together, these findings highlight the potential utility and limitations of phage therapy to treat antibiotic-resistant enterococcal infections.

IMPORTANCE

Phage therapy is an emerging therapeutic approach for treating bacterial infections that do not respond to traditional antibiotics. The addition of phage therapy to systemic antibiotics to treat a patient with recurrent E. faecium infections that were non-responsive to antibiotics alone resulted in fewer hospitalizations and improved the patient's quality of life. Combination phage and antibiotic therapy reduced E. faecium and VRE abundance in the patient's stool. Eventually, an anti-phage antibody response emerged that was able to neutralize phage activity, which may have limited clinical efficacy. This study demonstrates the potential of phages as an additional option in the antimicrobial toolbox for treating invasive enterococcal infections and highlights the need for further investigation to ensure phage therapy can be deployed for maximum clinical benefit.

Harnessing the Diversity of Burkholderia spp. Prophages for Therapeutic Potential

Burkholderia spp. are often resistant to antibiotics, and infections with these organisms are difficult to treat. A potential alternative treatment for Burkholderia spp. infections is bacteriophage (phage) therapy; however, it can be difficult to locate phages that target these bacteria. Prophages incorporated into the bacterial genome have been identified within Burkholderia spp. and may represent a source of useful phages for therapy. Here, we investigate whether prophages within Burkholderia spp. clinical isolates can kill conspecific and heterospecific isolates. Thirty-two Burkholderia spp. isolates were induced for prophage release, and harvested phages were tested for lytic activity against the same 32 isolates. Temperate phages were passaged and their host ranges were determined, resulting in four unique phages of prophage origin that showed different ranges of lytic activity. We also analyzed the prophage content of 35 Burkholderia spp. clinical isolate genomes and identified several prophages present in the genomes of multiple isolates of the same species. Finally, we observed that Burkholdera cenocepacia isolates were more phage-susceptible than Burkholderia multivorans isolates. Overall, our findings suggest that prophages present within Burkholderia spp. genomes are a potentially useful starting point for the isolation and development of novel phages for use in phage therapy.

Structural insights into the molecular mechanism of high-level ceftazidime-avibactam resistance conferred by CMY-185

β-Lactamases can accumulate stepwise mutations that increase their resistance profiles to the latest β-lactam agents. CMY-185 is a CMY-2-like β-lactamase and was identified in an Escherichia coli clinical strain isolated from a patient who underwent treatment with ceftazidime-avibactam. CMY-185, possessing four amino acid substitutions of A114E, Q120K, V211S, and N346Y relative to CMY-2, confers high-level ceftazidime-avibactam resistance, and accumulation of the substitutions incrementally enhances the level of resistance to this agent. However, the functional role of each substitution and their interplay in enabling ceftazidime-avibactam resistance remains unknown. Through biochemical and structural analysis, we present the molecular basis for the enhanced ceftazidime hydrolysis and impaired avibactam inhibition conferred by CMY-185. The substituted Y346 residue is a major driver of the functional evolution as it rejects primary avibactam binding due to the steric hindrance and augments oxyimino-cephalosporin hydrolysis through a drastic structural change, rotating the side chain of Y346 and then disrupting the H-10 helix structure. The other substituted residues E114 and K120 incrementally contribute to rejection of avibactam inhibition, while S211 stimulates the turnover rate of the oxyimino-cephalosporin hydrolysis. These findings indicate that the N346Y substitution is capable of simultaneously expanding the spectrum of activity against some of the latest β-lactam agents with altered bulky side chains and rejecting the binding of β-lactamase inhibitors. However, substitution of additional residues may be required for CMY enzymes to achieve enhanced affinity or turnover rate of the β-lactam agents leading to clinically relevant levels of resistance.IMPORTANCECeftazidime-avibactam has a broad spectrum of activity against multidrug-resistant Gram-negative bacteria including carbapenem-resistant Enterobacterales including strains with or without production of serine carbapenemases. After its launch, emergence of ceftazidime-avibactam-resistant strains that produce mutated β-lactamases capable of efficiently hydrolyzing ceftazidime or impairing avibactam inhibition are increasingly reported. Furthermore, cross-resistance towards cefiderocol, the latest cephalosporin in clinical use, has been observed in some instances. Here, we clearly demonstrate the functional role of the substituted residues in CMY-185, a four amino-acid variant of CMY-2 identified in a patient treated with ceftazidime-avibactam, for high-level resistance to this agent and low-level resistance to cefiderocol. These findings provide structural insights into how β-lactamases may incrementally alter their structures to escape multiple advanced β-lactam agents.

Harnessing the diversity of Burkholderia spp. prophages for therapeutic potential

Burkholderia spp. are often resistant to antibiotics, and infections with these organisms are difficult to treat. A potential alternative treatment for Burkholderia spp. infections is bacteriophage (phage) therapy; however, it can be difficult to locate phages that target these bacteria. Prophages incorporated into the bacterial genome have been identified within Burkholderia spp. and may represent a source of useful phages for therapy. Here we investigate whether prophages within Burkholderia spp. clinical isolates can kill conspecific and heterospecific isolates. Thirty-two Burkholderia spp. isolates were induced for prophage release, and harvested prophages were tested for lytic activity against the same 32 isolates. Lytic phages were passaged and their host ranges were determined, resulting in four unique phages of prophage origin that showed different ranges of lytic activity. We also analyzed the prophage content of 35 Burkholderia spp. clinical isolate genomes, and identified several prophages present in the genomes of multiple isolates of the same species. Finally, we observed that B. cenocepacia isolates were more phage-susceptible than Burkholderia multivorans isolates. Overall, our findings suggest that prophages present within Burkholderia spp. genomes are a potentially useful starting point for the isolation and development of novel phages for use in phage therapy.

In vitro activity of clindamycin, doxycycline, and trimethoprim/sulfamethoxazole against clinical isolates of β-hemolytic Streptococcus spp. via BD Phoenix and broth microdilution

We tested 85 isolates of β-hemolytic Streptococcus spp. against trimethoprim/sulfamethoxazole (TMP/SMX), clindamycin, and doxycycline by broth microdilution (BMD) and BD Phoenix. Susceptibility rates via BMD for TMP/SMX, clindamycin, and doxycycline were 100%, 85.5%, and 56.6%, respectively. TMP/SMX is a potential monotherapy agent for β-hemolytic Streptococcus skin and soft tissue infections.

Stewardship-Guided T2Candida Testing Shortens Time to Antifungal Treatment and Reduces Antifungal Usage Among Medical Intensive Care Unit Patients With Septic Shock

Background

Diagnosis of invasive candidiasis (IC) is limited by insensitivity and slow turnaround of cultures. Our objectives were to define the performance of T2Candida, a nonculture test, under guidance of a diagnostic stewardship program, and evaluate impact on time to antifungal initiation and antifungal utilization.

Methods

This was a retrospective study of adult medical intensive care unit (MICU) patients with septic shock for whom T2Candida testing was performed from March 2017 to March 2020. Patients with positive T2Candida results during this period were compared to MICU patients who did not undergo T2Candida testing but had septic shock and blood cultures positive for Candida from January 2016 through March 2020.

Results

Overall, 155 T2Candida tests from 143 patients were included. Nine percent of T2Candida tests were positive compared to 4.5% of blood cultures. Sensitivity, specificity, positive predictive value, and negative predictive value of T2Candida for proven and probable IC were 78%, 95%, 50%, and 99%, respectively. Patients who tested positive for T2Candida (n = 14) were diagnosed earlier and initiated on antifungal therapy sooner than patients with IC (n = 14) diagnosed by blood culture alone (median, 5.6 vs 60 hours; P < .0001). Median antifungal days of therapy/1000 patient-days were 23.3/month preimplementation and 15/month postimplementation (P  = .007). Following a negative T2Candida result, empiric antifungals were either not administered in 58% or discontinued within 72 hours in 96% of patients.

Conclusions

Diagnostic stewardship guided T2Candida testing resulted in reduced time to IC diagnosis, faster initiation of antifungal therapy, and lower antifungal usage among MICU patients with septic shock.

Serratia endocarditis: antimicrobial management strategies and clinical outcomes

OBJECTIVES

The incidence of Serratia endocarditis is increasing, yet optimal treatment has not been defined. Our objective was to investigate the outcomes of patients with Serratia endocarditis by treatment strategy.

METHODS

We reviewed adult patients with definitive Serratia endocarditis at two independent health systems between July 2001 and April 2023. Combination therapy was defined as receipt of ≥2 in vitro active agents for ≥72 h.

RESULTS

Seventy-five patients were included; 64% (48/75) were male and 85% (64/75) were people who inject drugs. Compared with monotherapy, receipt of combination therapy was associated with lower rates of microbiological failure (0% versus 15%, P = 0.026) and 90 day all-cause mortality (11% versus 31%, P = 0.049). Antimicrobial discontinuation due to an adverse event was more common among patients receiving combination therapy compared with monotherapy (36% versus 8%, P = 0.058).

CONCLUSIONS

In the largest series of Serratia endocarditis to date, combination antibiotic treatment was associated with improved outcomes. However, larger, prospective studies are warranted.

High-level ceftazidime/avibactam resistance in Escherichia coli conferred by the novel plasmid-mediated β-lactamase CMY-185 variant

OBJECTIVES

To characterize a blaCMY variant associated with ceftazidime/avibactam resistance from a serially collected Escherichia coli isolate.

METHODS

A patient with an intra-abdominal infection due to recurrent E. coli was treated with ceftazidime/avibactam. On Day 48 of ceftazidime/avibactam therapy, E. coli with a ceftazidime/avibactam MIC of >256 mg/L was identified from abdominal drainage. Illumina and Oxford Nanopore Technologies WGS was performed on serial isolates to identify potential resistance mechanisms. Site-directed mutants of CMY β-lactamase were constructed to identify amino acid residues responsible for ceftazidime/avibactam resistance.

RESULTS

WGS revealed that all three isolates were E. coli ST410. The ceftazidime/avibactam-resistant strain uniquely acquired a novel CMY β-lactamase gene, herein called blaCMY-185, harboured on an IncI-γ/K1 conjugative plasmid. The CMY-185 enzyme possessed four amino acid substitutions relative to CMY-2, including A114E, Q120K, V211S and N346Y, and conferred high-level ceftazidime/avibactam resistance with an MIC of 32 mg/L. Single CMY-2 mutants did not confer reduced ceftazidime/avibactam susceptibility. However, double and triple mutants containing N346Y previously associated with ceftazidime/avibactam resistance in other AmpC enzymes, conferred ceftazidime/avibactam MICs ranging between 4 and 32 mg/L as well as reduced susceptibility to the newly developed cephalosporin, cefiderocol. Molecular modelling suggested that the N346Y substitution confers the reduction of avibactam inhibition due to steric hindrance between the side chain of Y346 and the sulphate group of avibactam.

CONCLUSIONS

We identified ceftazidime/avibactam resistance in E. coli associated with a novel CMY variant. Unlike other AmpC enzymes, CMY-185 appears to require an additional substitution on top of N346Y to confer ceftazidime/avibactam resistance.

Mutations in ompK36 differentially impact in vitro synergy of meropenem/vaborbactam and ceftazidime/avibactam in combination with other antibiotics against KPC-producing Klebsiella pneumoniae

Objectives

Ceftazidime/avibactam and meropenem/vaborbactam are preferred agents for Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-Kp) infections and are often used in combination with other agents. We aimed to characterize the synergy of combinations against KPC-Kp with varying ompK36 genotypes.

Methods

KPC-Kp that harboured ompK36 WT, IS5 or glycine-aspartic acid duplication (GD) genotypes were selected. MICs were determined in triplicate. Synergy was assessed by time-kill assays for ceftazidime/avibactam and meropenem/vaborbactam in combination with colistin, gentamicin, tigecycline, meropenem or fosfomycin against 1 × 108 cfu/mL KPC-Kp.

Results

KPC-Kp harboured ompK36 WT (n = 5), IS5 (n = 5) or GD (n = 5); 11 were KPC-2 and 4 were KPC-3. All were susceptible to ceftazidime/avibactam and meropenem/vaborbactam. In time-kill analysis, ceftazidime/avibactam and meropenem/vaborbactam 1 × MIC exhibited mean 24 h log-kills of -2.01 and -0.84, respectively. Ceftazidime/avibactam was synergistic in combination with colistin independent of ompK36 genotype. Ceftazidime/avibactam combinations impacted by porin mutations (compared to WT) were meropenem (-5.18 versus -6.62 mean log-kill, P < 0.001) and fosfomycin (-3.98 versus -6.58, P = 0.058). Mean log-kills with meropenem/vaborbactam were greatest in combination with gentamicin (-5.36). In the presence of porin mutations, meropenem/vaborbactam killing activity was potentiated by the addition of colistin (-6.65 versus -0.70, P = 0.03) and fosfomycin (-3.12 versus 1.54, P = 0.003).

Conclusions

Our results shed new light on the synergy of ceftazidime/avibactam and meropenem/vaborbactam combinations against KPC-Kp with or without porin mutations. Killing activity of ceftazidime/avibactam with other cell wall active agents was decreased against isolates with porin mutations. On the other hand, some meropenem/vaborbactam combinations demonstrated enhanced killing in the presence of porin mutations.

In vitro activity of cefiderocol against Pseudomonas aeruginosa demonstrating evolved resistance to novel β-lactam/β-lactamase inhibitors

Background

Cefiderocol demonstrates excellent activity against MDR Pseudomonas aeruginosa; however, the activity against isolates from patients previously treated with β-lactam agents is unknown. We aimed to determine the activity of cefiderocol against P. aeruginosa collected before and after treatment with traditional β-lactams and new β-lactam/β-lactamase inhibitors.

Methods

Cefiderocol MICs were determined in triplicate in iron-depleted cation-adjusted Mueller-Hinton broth and compared with β-lactam MICs tested by standard methods. All isolates underwent WGS analysis to identify mutations associated with resistance.

Results

One hundred and seventy-eight P. aeruginosa isolates were evaluated; 48% (86/178) were non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam. The cefiderocol MIC50 and MIC90 were 0.12 and 1 mg/L, respectively. Median cefiderocol MICs did not vary against isolates classified as MDR, XDR, or those non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam when compared with non-MDR isolates. Against isolates collected from patients previously treated with ceftolozane/tazobactam, cefiderocol MICs were increased 4-fold compared with baseline. Cross-resistance to cefiderocol was identified in 21% (3/14) of patients who developed treatment-emergent resistance to ceftolozane/tazobactam. Overall, 6% (11/178) of isolates demonstrated cefiderocol MICs ≥2 mg/L, which were disproportionately collected from patients previously treated with ceftolozane/tazobactam (73%; 8/11). Isolates with reduced cefiderocol susceptibility harboured mutations in ampC, tonB-dependent receptors, the response regulator pirR and ftsI.

Conclusions

Cefiderocol demonstrates excellent in vitro activity against P. aeruginosa isolates exposed to other novel β-lactam agents; however, some exceptions were identified. Cross-resistance between cefiderocol and ceftolozane/tazobactam was evident, but not with ceftazidime/avibactam or imipenem/relebactam. Reduced cefiderocol susceptibility was mediated by mutations in ampC and tonB-dependent receptors.

Carbonic Anhydrase Inhibition as a Target for Antibiotic Synergy in Enterococci

Enterococcus faecalis is a hospital-associated opportunistic pathogen that can cause infections with high mortality, such as infective endocarditis. With an increasing occurrence of multidrug-resistant enterococci, there is a need for alternative strategies to treat enterococcal infections. We isolated a gentamicin-hypersusceptible E. faecalis strain from a patient with infective endocarditis that carried a mutation in the alpha-carbonic anhydrase (α-CA) and investigated how disruption of α-CA sensitized E. faecalis to killing with gentamicin. The gentamicin-hypersusceptible α-CA mutant strain showed increased intracellular gentamicin uptake in comparison to an isogenic strain encoding full-length, wild-type α-CA. We hypothesized that increased gentamicin uptake could be due to increased proton motive force (PMF), increased membrane permeability, or both. We observed increased intracellular ATP production in the α-CA mutant strain, suggesting increased PMF-driven gentamicin uptake contributed to the strain's gentamicin susceptibility. We also analyzed the membrane permeability and fatty acid composition of isogenic wild-type and α-CA mutant strains and found that the mutant displayed a membrane composition that was consistent with increased membrane permeability. Finally, we observed that exposure to the FDA-approved α-CA inhibitor acetazolamide lowered the gentamicin MIC of eight genetically diverse E. faecalis strains with intact α-CA but did not change the MIC of the α-CA mutant strain. These results suggest that α-CA mutation or inhibition increases PMF and alters membrane permeability, leading to increased uptake of gentamicin into E. faecalis. This connection could be exploited clinically to provide new combination therapies for patients with enterococcal infections. IMPORTANCE Enterococcal infections can be difficult to treat, and new therapeutic approaches are needed. In studying an E. faecalis clinical strain from an infected patient, we found that the bacteria were rendered hypersusceptible to aminoglycoside antibiotics through a mutation that disrupted the α-CA. Our follow-on work suggested two different ways that α-CA disruption causes increased gentamicin accumulation in E. faecalis: increased proton motive force-powered uptake and increased membrane permeability. We also found that a mammalian CA inhibitor could sensitize a variety of E. faecalis strains to killing with gentamicin. Given that mammalian CA inhibitors are frequently used to treat conditions such as glaucoma, hypertension, and epilepsy, our findings suggest that these "off-the-shelf" inhibitors could also be useful partner antibiotics for the treatment of E. faecalis infections.

Impact of Rapid Identification and Stewardship Intervention on Coagulase-Negative Staphylococcus Bloodstream Infection

We investigated the impact of rapid diagnostic testing with and without algorithm-based stewardship recommendations on antibiotic use for bloodstream infection with coagulase-negative staphylococci. A significant reduction in antibiotic days of therapy was achieved in the stewardship intervention group that was not seen with rapid diagnostic testing alone.

Antimicrobial Agents and Chemotherapy Launches a New Section Focused on Innovative Antimicrobial Stewardship Studies

In response to the global burden of antimicrobial resistance (AMR) and the critical role antimicrobial stewardship plays in optimizing antibiotic use and reducing the subsequent emergence of AMR, Antimicrobial Agents and Chemotherapy is excited to add a new section to the journal focused on antimicrobial stewardship studies. Combatting the devastating burden of AMR requires novel, multipronged approaches from clinicians and scientists alike. Launching this new section is an important step in disseminating cutting-edge research that will have notable implications in the global fight against antimicrobial-resistant pathogens.

Clindamycin Plus Vancomycin Versus Linezolid for Treatment of Necrotizing Soft Tissue Infection

Background

Necrotizing soft tissue infections (NSTIs) are life-threatening infections. The aim of this study is to evaluate the safety of clindamycin plus vancomycin versus linezolid as empiric treatment of NSTIs.

Methods

This was a retrospective, single-center, quasi-experimental study of patients admitted from 1 June 2018 to 30 June 2019 (preintervention) and 1 May 2020 to 15 October 2021 (postintervention). Patients who received surgical management within 24 hours of NSTI diagnosis and at least 1 dose of linezolid or clindamycin were included. The primary endpoint was death at 30 days. The secondary outcomes included rates of acute kidney injury (AKI) and Clostridioides difficile infection (CDI).

Results

A total of 274 patients were identified by admission diagnosis code for NSTI or Fournier gangrene; 164 patients met the inclusion criteria. Sixty-two matched pairs were evaluated. There was no difference in rates of 30-day mortality (8.06% vs 6.45%; hazard ratio [HR], 1.67 [95% confidence interval {CI}, .32-10.73]; P = .65). There was no difference in CDI (6.45% vs 1.61%; HR, Infinite [Inf], [95% CI, .66-Inf]; P = .07) but more AKI in the preintervention group (9.68% vs 1.61%; HR, 6 [95% CI, .73-276]; P = .05).

Conclusions

In this small, retrospective, single-center, quasi-experimental study, there was no difference in 30-day mortality in patients receiving treatment with clindamycin plus vancomycin versus linezolid in combination with standard gram-negative and anaerobic therapy and surgical debridement for the treatment of NSTIs. A composite outcome of death, AKI, or CDI within 30 days was more common in the clindamycin plus vancomycin group.

Navigating Available Treatment Options for Carbapenem-Resistant Acinetobacter baumannii-calcoaceticus Complex Infections

Carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRAB) is one of the top-priority pathogens for new antibiotic development. Unlike other antibiotic-resistant threats, none of the available therapies have been shown to consistently reduce mortality or improve patient outcomes in clinical trials. Antibiotic combination therapy is routinely used in clinical practice; however, the preferred combination has not been defined. This narrative review focuses on evidence-based solutions for the treatment of invasive CRAB infections. We dissect the promise and perils of traditional agents used in combination, such as colistin, sulbactam, and the tetracyclines, and offer clinical pearls based on our interpretation of the available data. Next, we investigate the merits of newly developed β-lactam agents like cefiderocol and sulbactam-durlobactam, which have demonstrated contrasting results in recent randomized clinical trials. The review concludes with the authors' perspective on the evolving treatment landscape for CRAB infections, which is complicated by limited clinical data, imperfect treatment options, and a need for future clinical trials. We propose that effective treatment for CRAB infections requires a personalized approach that incorporates host factors, the site of infection, pharmacokinetic-pharmacodynamic principles, local molecular epidemiology of CRAB isolates, and careful interpretation of antibiotic susceptibility testing results. In most clinical scenarios, a dose-optimized, sulbactam-based regimen is recommended with the addition of at least one other in vitro active agent. Should sulbactam-durlobactam receive regulatory approval, recommendations will need to be re-evaluated with the most recent evidence.

Microbiologic and Clinical description of Post-operative Central Nervous System Infection following Endoscopic Endonasal Surgery

INTRODUCTION

Consensus guidelines for antibiotic prophylaxis in Endoscopic endonasal surgery (EES) have not been developed. The study objective was to define the microbiologic and clinical characteristics of post-EES central nervous system (CNS) infections METHODS: This was a single center, retrospective study of patients >18 years of age who underwent EES between 1/2010 and 7/2021 at a high-volume skull base center. Patients with confirmed CNS infection within 30 days of EES were included. During the study period, the standard prophylaxis regimen was ceftriaxone 2g every 12 hours for 48 hours. For patients with a documented penicillin allergy, vancomycin plus aztreonam was recommended.

RESULTS

In total 2,440 EES procedures were performed on 2,005 patients; the CNS infection rate was 1.8% (37/2005). CNS infections were more common among patients with a history of prior EES (6.5% [20/307]) compared to those who did not (1% [17/1698]; P<0.001). The median time from EES to CNS infection was 12 (6-19) days. Thirty-two percent (12/37) of CNS infections were polymicrobic, which was more common among patients without prior EES (52.9% [9/17]) compared to those with prior EES (15% [3/20]; P=0.03). Across all cases, S. aureus (n=10) and P. aeruginosa (n=8) were commonly isolated pathogens. Among those with confirmed MRSA nares colonization prior to EES, 75% (3/4) developed MRSA CNS infections compared to 6.1% (2/33) of non-colonized patients (P=0.005).

CONCLUSIONS

CNS infection post-EES is rare and causative pathogens vary. Further studies are needed to identify the impact of MRSA nares screening on antimicrobial prophylaxis prior to EES.

Early initiation of three-drug combinations for the treatment of carbapenem-resistant A. baumannii among COVID-19 patients

OBJECTIVES

We evaluated the clinical characteristics and outcomes of patients with COVID-19 who received three-drug combination regimens for treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) infections during a single-centre outbreak. Our objective was to describe the clinical outcomes and molecular characteristics and in vitro synergy of antibiotics against CRAB isolates.

MATERIALS AND METHODS

Patients with severe COVID-19 admitted between April and July 2020 with CRAB infections were retrospectively evaluated. Clinical success was defined as resolution of signs/symptoms of infection without need for additional antibiotics. Representative isolates underwent whole-genome sequencing (WGS) and in vitro synergy of two- or three-drug combinations was assessed by checkerboard and time-kill assays, respectively.

RESULTS

Eighteen patients with CRAB pneumonia or bacteraemia were included. Treatment regimens included high-dose ampicillin-sulbactam, meropenem, plus polymyxin B (SUL/MEM/PMB; 72%), SUL/PMB plus minocycline (MIN; 17%) or other combinations (12%). Clinical resolution was achieved in 50% of patients and 30-day mortality was 22% (4/18). Seven patients had recurrent infections, during which further antimicrobial resistance to SUL or PMB was not evident. PMB/SUL was the most active two-drug combination by checkerboard. Paired isolates collected before and after treatment with SUL/MEM/PMB did not demonstrate new gene mutations or differences in the activity of two- or three-drug combinations.

CONCLUSIONS

Use of three-drug regimens for severe CRAB infections among COVID-19 resulted in high rates of clinical response and low mortality relative to previous studies. The emergence of further antibiotic resistance was not detected phenotypically or through WGS analysis. Additional studies are needed to elucidate preferred antibiotic combinations linked to the molecular characteristics of infecting strains.

Phage therapy in a lung transplant recipient with cystic fibrosis infected with multidrug-resistant Burkholderia multivorans

BACKGROUND

There is increased interest in bacteriophage (phage) therapy to treat infections caused by antibiotic-resistant bacteria. A lung transplant recipient with cystic fibrosis and Burkholderia multivorans infection was treated with inhaled phage therapy for 7 days before she died.

METHODS

Phages were given via nebulization through the mechanical ventilation circuit. Remnant respiratory specimens and serum were collected. We quantified phage and bacterial deoxyribonucleic acid (DNA) using quantitative polymerase chain reaction, and tested phage neutralization in the presence of patient serum. We performed whole genome sequencing and antibiotic and phage susceptibility testing on 15 B. multivorans isolates. Finally, we extracted lipopolysaccharide (LPS) from two isolates and visualized their LPS using gel electrophoresis.

RESULTS

Phage therapy was temporally followed by a temporary improvement in leukocytosis and hemodynamics, followed by worsening leukocytosis on day 5, deterioration on day 7, and death on day 8. We detected phage DNA in respiratory samples after 6 days of nebulized phage therapy. Bacterial DNA in respiratory samples decreased over time, and no serum neutralization was detected. Isolates collected between 2001 and 2020 were closely related but differed in their antibiotic and phage susceptibility profiles. Early isolates were not susceptible to the phage used for therapy, while later isolates, including two isolates collected during phage therapy, were susceptible. Susceptibility to the phage used for therapy was correlated with differences in O-antigen profiles of an early versus a late isolate.

CONCLUSIONS

This case of clinical failure of nebulized phage therapy highlights the limitations, unknowns, and challenges of phage therapy for resistant infections.

Impact of ompk36 genotype and KPC subtype on the in vitro activity of ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam against KPC-producing K. pneumoniae clinical isolates

Objectives

The availability of new β-lactam/β-lactamase inhibitors ceftazidime/avibactam, meropenem/vaborbactam and imipenem/relebactam have redefined contemporary treatment of Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) infections. We aimed to characterize and contrast the in vitro activity of these agents against genetically diverse KPC-Kp clinical isolates.

Methods

We analysed genomes of 104 non-consecutive KPC-Kp isolates and compared the in vitro antibiotic activity by KPC subtype and ompK36 genotype. MICs were determined in triplicate by CLSI methods. Twenty representative isolates were selected for time–kill analyses against physiological steady-state and trough concentrations, as well as 4× MIC for each agent.

Results

Fifty-eight percent and 42% of isolates harboured KPC-2 and KPC-3, respectively. OmpK36 mutations were more common among KPC-2- compared with KPC-3-producing Kp (P < 0.0001); mutations were classified as IS5 insertion, glycine-aspartic acid insertion at position 134 (GD duplication) and other mutations. Compared to isolates with WT ompK36, ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam MICs were elevated for isolates with IS5 by 2-, 4- and 16-fold, respectively (P < 0.05 for each). Against isolates with GD duplication, imipenem/relebactam and meropenem/vaborbactam MICs were increased, but ceftazidime/avibactam MICs were not. In time–kill studies, ceftazidime/avibactam-mediated killing correlated with ceftazidime/avibactam MICs, and did not vary across ompK36 genotypes. Imipenem/relebactam was not bactericidal against any isolate at trough concentrations. At steady-state imipenem/relebactam concentrations, regrowth occurred more commonly for isolates with IS5 mutations. Log-kills were lower in the presence of meropenem/vaborbactam for isolates with GD duplication compared with IS5 mutations.

Conclusions

Our investigation identified key genotypes that attenuate, to varying degrees, the in vitro activity for each of the new β-lactam/β-lactamase inhibitors. Additional studies are needed to translate the importance of these observations into clinical practice.

Evolution and Transmission of Cefiderocol-Resistant Acinetobacter baumannii During an Outbreak in the Burn Intensive Care Unit

We report on 11 critically ill burn patients treated with cefiderocol for carbapenem-resistant Acinetobacter baumannii infections. Clinical success was achieved in 36% and complicated by treatment-emergent resistance and interpatient transmission of cefiderocol-resistant A. baumannii. Resistant isolates harbored disrupted pirA and piuA genes that were not disrupted among susceptible isolates.

High-level ceftazidime-avibactam resistance in Escherichia coli conferred by the novel plasmid-mediated beta-lactamase CMY-185 variant

Objectives

To characterize a bla CMY variant associated with ceftazidime-avibactam (CZA) resistance from a serially collected Escherichia coli isolate.

Methods

A patient with an intra-abdominal infection due to recurrent E. coli was treated with CZA. On day 48 of CZA therapy, E. coli with a CZA MIC of >256 mg/L was identified from abdominal drainage. Illumina WGS was performed on all isolates to identify potential resistance mechanisms. Site-directed mutants of CMY β-lactamase were constructed to identify amino acid residues responsible for CZA resistance.

Results

WGS revealed that all three isolates were E. coli ST410. The CZA-resistant strain uniquely acquired a novel CMY β-lactamase gene, herein called bla CMY-185 , harbored on an IncIγ-type conjugative plasmid. The CMY-185 enzyme possessed four amino acid substitutions relative to CMY-2 including A114E, Q120K, V211S, and N346Y and conferred high-level CZA resistance with an MIC of 32 mg/L. Single CMY-2 mutants did not confer reduced CZA susceptibility. However, double and triple mutants containing N346Y previously associated with CZA resistance in other AmpC enzymes, conferred CZA MICs ranging between 4 and 32 mg/L as well as reduced susceptibility to the newly developed cephalosporin, cefiderocol. Molecular modelling suggested that the N346Y substitution confers the reduction of avibactam inhibition due to the steric hindrance between the side chain of Y346 and the sulfate group of avibactam.

Conclusion

We identified CZA resistance in E. coli associated with a novel CMY variant. Unlike other AmpC enzymes, CMY-185 appears to require an additional substitution on top of N346Y to confer CZA resistance.

Epidemiology and Clinical Outcomes of non-HACEK Gram-negative Infective Endocarditis

Background

The objectives of this study were to describe the changing epidemiology of GNIE and identify factors associated with treatment failure and death.

Methods

Adult patients with GNIE were included if they met modified Duke criteria for definitive IE between April 2010 and December 2021. Patients were identified using Boolean Search terms. Clinical failure was a defined as a composite of all-cause 42-day mortality or microbiologic failure. All analyses were performed using Stata version 15.1.

Results

One-hundred twenty-three patients were included. The most common pathogens were Serratia spp. (43%), Pseudomonas aeruginosa (21%), and Klebsiella spp. (14%). Fifty-two percent of cases were among persons who injection drugs (PWID; n=64) for whom Serratia spp. (70%) was the most common cause of GNIE. Overall, patients infected with P. aeruginosa had higher microbiologic failure rates than other patients (23% vs 6%; P=0.004). Patients who received combination therapy (n=53) had comparable median lengths of stay (23 days vs 19.5, P=0.412), microbiologic failure rates (11.3% vs 7.1%, P=0.528), clinical failure rates (18.9% vs 22.9%, P=0.592), and 90-day mortality rates (13.2% vs 25.7%, P=0.088) as those treated with monotherapy. After applying stepwise logistic regression, male gender, Pitt Bacteremia Score, and not receiving surgical intervention despite a surgical indication were associated with clinical failure.

Conclusions

This is the first study to identify Serratia spp. as the most common etiology of GNIE, which was particularly true among PWID. Microbiologic failures occurred most commonly among P. aeruginosa, and use of combination antimicrobial therapy did not improve clinical outcomes.

Within-Host Genotypic and Phenotypic Diversity of Contemporaneous Carbapenem-Resistant Klebsiella pneumoniae from Blood Cultures of Patients with Bacteremia

It is unknown whether bacterial bloodstream infections (BSIs) are commonly caused by single organisms or mixed microbial populations. We hypothesized that contemporaneous carbapenem-resistant Klebsiella pneumoniae (CRKP) strains from blood cultures of individual patients are genetically and phenotypically distinct. We determined short-read whole-genome sequences of 10 sequence type 258 (ST258) CRKP strains from blood cultures in each of 6 patients (Illumina HiSeq). Strains clustered by patient by core genome and pan-genome phylogeny. In 5 patients, there was within-host strain diversity by gene mutations, presence/absence of antibiotic resistance or virulence genes, and/or plasmid content. Accessory gene phylogeny revealed strain diversity in all 6 patients. Strains from 3 patients underwent long-read sequencing for genome completion (Oxford Nanopore) and phenotypic testing. Genetically distinct strains within individuals exhibited significant differences in carbapenem and other antibiotic responses, capsular polysaccharide (CPS) production, mucoviscosity, and/or serum killing. In 2 patients, strains differed significantly in virulence during mouse BSIs. Genetic or phenotypic diversity was not observed among strains recovered from blood culture bottles seeded with index strains from the 3 patients and incubated in vitro at 37°C. In conclusion, we identified genotypic and phenotypic variant ST258 CRKP strains from blood cultures of individual patients with BSIs, which were not detected by the clinical laboratory or in seeded blood cultures. The data suggest a new paradigm of CRKP population diversity during BSIs, at least in some patients. If validated for BSIs caused by other bacteria, within-host microbial diversity may have implications for medical, microbiology, and infection prevention practices and for understanding antibiotic resistance and pathogenesis. IMPORTANCE The long-standing paradigm for pathogenesis of bacteremia is that, in most cases, a single organism passes through a bottleneck and establishes itself in the bloodstream (single-organism hypothesis). In keeping with this paradigm, standard practice in processing positive microbiologic cultures is to test single bacterial strains from morphologically distinct colonies. This study is the first genome-wide analysis of within-host diversity of Klebsiella pneumoniae strains recovered from individual patients with bloodstream infections (BSIs). Our finding that positive blood cultures comprised genetically and phenotypically heterogeneous carbapenem-resistant K. pneumoniae strains challenges the single-organism hypothesis and suggests that at least some BSIs are caused by mixed bacterial populations that are unrecognized by the clinical laboratory. The data support a model of pathogenesis in which pressures in vivo select for strain variants with particular antibiotic resistance or virulence attributes and raise questions about laboratory protocols and treatment decisions directed against single strains.

1737. Xeruborbactam (QPX) Potentiates the Activity of β-Lactam (BL) Antibiotics Against a Diverse Group of Highly Drug-Resistant Enterobacterales (ENT)

Background

Antibiotic resistant ENT are a growing threat worldwide. QPX is an ultra-broad-spectrum β-lactamase inhibitor (BLI) with potent inhibition of classes A and D, and many metallo-β-lactamases, which has potential to fill the void of currently available BL-BLIs.

Methods

We evaluated QPX (fixed concentration of 8 µg/mL) in combination with meropenem (MEM), cefepime (FEP) and aztreonam (ATM) against a diverse group of ENT clinical isolates selected from a worldwide repository. Antibiotic resistance determinants were assessed by mining whole-genome sequencing data generated using Illumina MiSeq.

Results

Klebsiella spp, Enterobacter spp, and Escherichia coli were most common among the 90 isolates tested (Fig. 1). 71% (64) produced carbapenemases (Fig. 2): 3 isolates produced both class A and B carbapenemases. 11% of isolates harbored mutations in ompK 36/ompC genes. 57% (51) were resistant to MEM, 31% to imipenem-relebactam, 17% (15) to ceftazidime-avibactam (CZA), and 9% to MEM-vaborbactam (MVB). ENT-resistant to CZA were due to production of class B, D or KPC-3 variants, or ompC mutation in a K. aerogenes isolate. ENT-resistant to MVB were due to class B or D enzymes, or class A with ompK36 or ompC mutations. MIC distributions of BL with or without QPX against all isolates tested are presented in Fig. 3. Addition of QPX to MEM, FEP and AMT reduced MIC50s and MIC90s of these agents (Fig. 3; p&lt; 0.0001). Of note, addition of QPX reduced MEM MICs more than did vaborbactam (median 533- versus 24-fold; p=0.0006). QPX reduced MICs of MEM, FEP and ATM to levels below respective breakpoints for non-susceptibility (Fig. 3). MIC distribution of ENT isolates stratified by the types of carbapenemases are presented in Fig. 4. QPX potentiated activity of MEM, FEP or ATM against ENT, regardless of whether they produced class A, B or D carbapenemases.

Conclusion

QPX enhanced activity of MEM, FEP and ATM against carbapenemase-producing or other carbapenem-resistant ENT (CRE), regardless of species or other resistance determinants. Most remarkably, QPX rendered each BL equally active against CRE. The expanded spectrum of QPX against class B and D carbapenemases addresses a major unmet need against CRE.

Disclosures

Cornelius J. Clancy, MD, receives research funding paid to his institution from Astellas and Merck: Grant/Research Support|serves as an advisory Board member for Astellas, Cidara, and Scynexis, served on the advisory board for Merck, Qpex Biopharma, and Shionogi: Advisor/Consultant|Venatorx and Needham & Associates: Advisor/Consultant.

589. Clinical Outcomes of Twice versus Thrice daily Metronidazole Dosing for Bacteroides Bloodstream Infections

Background

The optimal metronidazole dose for the treatment of Bacteroides spp. has not been defined. The purpose of this study was to evaluate the utility of a twice (BID), rather than thrice (TID) daily metronidazole dosing strategy among patients with bacteremia due to Bacteroides spp.

Methods

Adult, hospitalized patients with bacteremia secondary to Bacteroides spp. between October 2010 and June 2021 were assessed across 11 hospitals. The primary endpoint was clinical failure which was a composite of all-cause 30-day mortality, escalation of antimicrobial therapy, 30-day readmission or recurrence due to an anaerobic infection, positive repeat blood cultures for Bacteroides spp., or failure to resolve leukocytosis or fever.

Results

208 patients were included; 68 received metronidazole 500mg BID and 140 patients received metronidazole 500mg TID (Figure). Patient age, Charlson comorbidity index, and Pitt Bacteremia score were similar among patients receiving BID vs TID dosing (Table 1). On balance, patients who received BID dosing were more likely to receive oral metronidazole and had shorter lengths of hospitalization prior to bacteremia. Overall, there was no significant difference between rates of clinical failure or other outcomes between patients who received BID versus TID metronidazole dosing (Table 2). In the multivariate model, neither the use of TID dosing (OR = 0.74; 95% CI = 0.33–1.65; P=0.457), time to treatment initiation (OR = 1; 95% CI = 0.81–1.22; P=0.968), days of initial non-metronidazole anaerobic therapy (OR = 0.91; 95% CI = 0.59–1.34; P=0.646), pre-infection length of stay (OR = 1.02; 95% CI = 0.99–1.05; P=0.106), admission prior to 2016 (OR = 1.09; 95% CI = 0.49–2.39; P=0.829), or initial oral metronidazole use (OR = 0.45; 95% CI = 0.18–1.03; P=0.066) were significantly associated with clinical failure. Figure 1:Inclusion and exclusion

Non-metronidazole anaerobic coverage consisted of a beta-lactam/beta-lactamase inhibitor, cefoxitin, or a carbapenem Table 1:Demographics and baseline characteristicsTable 2:Clinical outcomes*Patients were considered to have escalated antimicrobial therapy if, in the setting of ongoing signs of infections, antimicrobial therapy was either broadened or the frequency of metronidazole was increased from twice daily to thrice daily.

Conclusion

In the largest study to date of patients with Bacteroides spp. bacteremia treated with metronidazole, there was no significant difference between BID and TID metronidazole dosing strategies. In the absence of a clear benefit, metronidazole 500mg BID is a reasonable dosing strategy in lieu 500mg TID for infections due to Bacteroides spp.

Disclosures

Ryan K. Shields, PharmD, MS, Infectious Disease Connect: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Roche: Grant/Research Support.

916. Increased efficiency and impact of implementing ILUM insight within an antimicrobial stewardship program (ASP) at an academic medical center

Background

An ASP is mandated for all hospitals and requires extensive resources with multidisciplinary collaboration. We measured the impact of implementing real-time decision support software (ILUM Insight) within our ASP.

Methods

Our ASP has relied on prior authorization since 2002 and focused audit and feedback since 2015. In August 2021 we implemented to bring actionable data to front-line stewards. ILUM provides real-time notifications, organizes communications, and tracks patient-and provider-level data. We hypothesized that ILUM would increase the efficiency of ASP workflow and result in decreased antimicrobial utilization. We compared data 6 months before (8/20 – 1/21) and after (8/21 – 1/22) implementation. There were no significant staffing changes during either period.

Results

Existing notifications within ILUM were tailored to local practices, including alerts with intervention for positive blood cultures, antibiotic de-escalation, and bug-drug mismatches. New notifications were built for restricted antimicrobials, antibiotic timeouts, and MRSA screening. ASP pharmacists and physicians received training in July and November, respectively. A breakdown of all notifications received during the post-implementation period is provided in Fig 1. With increased ILUM usage, the number of interventions made by our ASP increased while missed opportunities decreased (Fig 2.). During the same time period, ASP communications rose from 205 to 1200 per month. Comparing pre- and post-implementation periods, antimicrobial days of therapy (DOT) per 1,000 patient days (PD) decreased by 14.5% from a median of 969 to 846 per month (Fig 3;P=0.002). Antimicrobial expenditures were decreased by a median 21% per month during the post-intervention period compared to baseline. Among patients prescribed antimicrobials during an index admission, 30-day re-admissions decreased from 330 to 262 and re-admissions associated with re-ordering of antimicrobials decreased from 235 to 182 (Fig 4).

Conclusion

Custom-designed, task-specific software improves the efficiency of daily ASP workflow and significantly decreased antimicrobial utilization without the need for additional ASP team members.

Disclosures

Ryan K. Shields, PharmD, MS, Infectious Disease Connect: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Roche: Grant/Research Support J Ryan Bariola, MD, Infectious Disease Connect: Salary support|Merck: Grant/Research Support Caley Yakemowicz, n/a, Infectious Disease Connect: Employee Courtney Simonick, n/a, Infectious Disease Connect: Stocks/Bonds Riaan Erwee, na, Infectious Disease Connect: Employee Erin K. McCreary, PharmD, Infectious Disease Connect: Advisor/Consultant Rima Abdel-Massih, MD, Infectious Disease Connect: Co founder and Chief Medical Officer|Infectious Disease Connect: Ownership Interest.

1030. Epidemiology and Microbiologic Characteristics of Post-operative Central Nervous System Infections following Endoscopic Endonasal Surgery

Background

Endoscopic Endonasal Surgery (EES) is an innovative surgical technique to remove brain tumors and lesions. Post-operative central nervous system (CNS) infections following EES are poorly described. The objective of this study was to define the epidemiology and characteristics of post-EES CNS infections.

Methods

Adult patients who underwent EES between 1/2010 and 7/2021 were evaluated and included if microbiologically confirmed CNS infection occurred within 30 days of EES. Suspected contaminants, ventricular drain colonization, and pre-EES CNS infections were excluded.

Results

Overall, 2005 patients underwent EES; 1.8% (37/2005) developed CNS infection. The median [IQR] age was 51 [42-60] years, 32.4% (12/37) were female, and 54% (20/37) had a prior EES. The most common indications for EES were tumor resection [67.6% (25/37)] and cerebrospinal fluid (CSF) leak repair [24.3% (9/37)]. Post-operative CSF leaks were documented in 70.3% (26/37) of patients and 24.3% (9/37) had an extra-ventricular drain or shunt in place for >48 hours at the time of infection. Ceftriaxone prophylaxis was prescribed in 64.9% (24/37) of cases and other regimens varied. The median [IQR] time from EES to diagnosis of CNS infection was 12 [6-19] days. The most common pathogens were S. aureus, Enterobacterales, and P. aeruginosa(Fig 1). Among 20 patients with prior EES, pathogens included S. aureus (5/20), Enterobacterales (3/20), Enterococcus spp. (3/20) and polymicrobic infections (3/20). Overall, 35.1% (13/37) of patients developed CNS infection due to a pathogen susceptible to pre-EES prophylaxis. Among those colonized with MRSA at time of EES, 75% (3/4) developed MRSA CNS infection compared to 6.1% (2/33) of non-colonized MRSA patients (P=0.005). The overall 30-day mortality rate was 2.7% (1/37). Figure:

1982. Epidemiology and Clinical Outcomes of non-HACEK Gram-negative Infective Endocarditis

Background

Infective endocarditis (IE) due to non-HACEK Gram-negative (GN) pathogens is rare, but optimal treatment has not yet been defined. The objective of this study was to report the epidemiology, clinical characteristics, and outcomes of GNIE across our health system.

Methods

Adult patients with GNIE were identified between April 2010 through December 2021 and included if they met DUKE criteria for definitive IE. Patients with persistently positive blood cultures for Gram-positive pathogens or yeast were excluded if valve cultures did not grow GN bacteria. Clinical failure was defined as a composite of all-cause mortality or microbiologic failure at day 42. Microbiologic failure was defined as an escalation of antimicrobial therapy after emergence of resistance, increased vegetation size, or failure to clear blood cultures by day 14.

Results

Overall, 123 patients were included. GN pathogens included Serratia spp. (43%), P. aeruginosa (21%), Klebsiella spp. (14%), and other GN bacteria (22%) (Figure). 64 (52%) cases were among persons who inject drugs (PWID) (Table 1). GNIE secondary to Serratia spp. was more common in PWID compared to other pathogens (85% vs 27%; P&lt; 0.001). Microbiologic failure was more common for P. aeruginosa than other pathogens (23% vs 5%; P=0.004). A stepwise multivariate logistic regression model identified age, PITT bacteremia score, and duration of positive blood cultures as independent predictors of clinical failure (Table 2). Patients who received &gt; 72 hours of combination therapy (n=53) had a comparable length of stay (23 days vs 19.5; P=0.412), microbiologic failure rate (11.3% vs 7.1%, P=0.528), clinical failure rate (18.9% vs 22.9%, P=0.592), and 90-day mortality rate (13.2% vs 25.7%, P=0.088) to those who did not receive combination therapy. 80% (4/5) of patients who experienced 30-day readmission secondary to an antimicrobial adverse event received combination therapy.

Table 1: Epidemiology and Overview CCI: Charleson Comorbidity Index; MDR: Multiple drug resistance; VGS: Viridans Group Streptococcus spp. #S. marcescens (n=50); S. liquefasciens (n=2); undifferentiated species (n=1) *K. pneumoniae (n=11); K. oxytoca (n=5); K. variicola (n=1); E. coli (n=12); P. mirabilis (n=3); P. vulgaris (n=1); E. cloacae complex (n=2); E. aerogenes (n=1) ^B. cepacia (n=2); S. maltophillia (n=2); A. lwoffi (n=2); P. stutzeri (n=1); A. baumanni (n=1) Table 2: Multivariate Logistic regression for factors associated with 42-day failure

Conclusion

To our knowledge this is the largest cohort of patients with non-HACEK GNIE, and the first to identify Serratia spp. to be the most common etiology of GNIE, particularly among PWID. Microbiologic failures occurred commonly among P. aeruginosa. Overall, we did not identify a clinical benefit to combination therapy; additional studies are needed to validate these findings.

Disclosures

Ryan K. Shields, PharmD, MS, Infectious Disease Connect: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Roche: Grant/Research Support.

912. Impact of Rapid Identification and Stewardship Intervention on Coagulase-negative Staphylococcus Bloodstream Infection (BSI)

Background

Coagulase-negative staphylococci (CoNS) are commonly isolated from blood cultures (BCx). Most do not require treatment (tx), yet antibiotics are frequently initiated. Workup of CoNS BSI consumes significant resources. We aimed to demonstrate the safety and efficacy of an early algorithm-based rapid diagnostic testing (RDT) plus antimicrobial stewardship (ASP) intervention.

Methods

BCx with CoNS were captured in 3 time periods to represent pre-RDT, RDT-only, and RDT+ASP. GenMark ePlex RDT was implemented for all Gram-positive BCx, identifying S. epidermidis and other non-aureus/lugdunensis Staphylococcal species. Results were called to ASP in both RDT-only and RDT+ASP periods. In the latter, a prospective algorithm was implemented to standardize ASP recommendations (Fig 1) for cases classified as simple, uncomplicated, and complicated BSI. The primary outcome was receipt of < 24h of antibiotic tx. Safety outcomes included rates of recurrent BSI and hospital readmission.

Results

184 patients were included (Fig 2). The median age was 62, 54% were male, and the median Charlson comorbidity index was 5. 41% had a central venous catheter at time of BSI. Overall, 67%, 19%, and 12% of cases were classified as simple, uncomplicated, or complicated BSI, respectively (Fig 3). BSI class and patient demographics did not vary between periods. During pre- and post-RDT periods, median days of antibiotic tx did not vary significantly for patients with simple BSI (1.1 vs 1.2). In contrast, median days of tx were reduced to 0 (P=0.005) for simple BSI in the RDT+ASP period. Overall, 54% of patients with CoNS BSI received < 24h of tx in RDT+ASP time period compared to 34% (P=0.009) in the combined pre-RDT and RDT-only periods. Tx was entirely avoided in 28% of CoNS BSI cases in the RDT+ASP period compared to 16.5% of cases in other periods (P=0.07). 7 cases classified as simple were reclassified as uncomplicated or complicated after further work up. Rates of recurrent BSI and 30-day readmission were comparable across time periods.

Conclusion

Our algorithm-based ASP + RDT intervention reduced antibiotic tx for CoNS BSI, an effect not realized with RDT alone. These data attest to the safety and efficacy of early ASP intervention for patients with CoNS BSI identified by RDTs at the time of positive BCx.

Disclosures

J Ryan Bariola, MD, Infectious Disease Connect: Salary support|Merck: Grant/Research Support Tina Khadem, PharmD, Infectious Disease Connect: Salary support|Merck: Grant/Research Support Brian Potoski, PharmD, BCPS-AQ ID, Merck Group: Grant/Research Support Ryan K. Shields, PharmD, MS, Infectious Disease Connect: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Roche: Grant/Research Support.

752. Decreased Echinocandin Resistance among Candida glabrata over an Eleven-Year Period at a University Hospital

Background

Invasive candidiasis (IC) is associated with significant morbidity and mortality. Echinocandins (ECH; caspofungin (CAS), micafungin (MFG), anidulafungin (AFG)) are first line therapy for IC. ECH resistance has emerged widely, most commonly among Candida glabrata. At some centers, > 10% of C. glabrata are ECH resistant. We reported ECH resistance in 8% of C. glabrata at our hospital from 2008–2014, which prompted stewardship strategies to limit prolonged ECH treatment courses. We evaluated trends of ECH resistance from Jan 2010-Dec 2020 among C. glabrata clinical isolates, and assayed isolates for FKS hot spot (HS) mutations.

Methods

We mined electronic medical records for ECH MIC data against C. glabrata clinical isolates at UPMC. We defined ECH resistance using Clinical and Laboratory Standards Institute clinical breakpoints. Isolates resistant to any ECH underwent FKS Sanger sequencing. Statistical analysis was performed using Stata.

Results

Overall CAS, AFG and MFG resistance rates among 516 isolates were 4%, 3%, and 2.5%, respectively. There was no significant difference in resistance rates between blood and non-blood sites (Table 1). There was a significant decrease in MFG resistance over the 12-year period (Fig 1). Time series regression analysis showed a decrease in rate of MFG resistance of 0.73% per year (p=.007). Trends for decreases in AFG and CAS resistance rates were also noted (p=.1 and p=.17). Similar analyses showed annual decreases in MFG MICs (0.019 μg/mL per year; p=.07). The average percentage of AFG resistant isolates was significantly lower in 2017–2020 than in 2012–2016 (p=.04); similar trends were evident for MFG (p=.07) and CAS (p=.08) (Fig 2). Sanger sequencing of FKS1/2 was performed for 27 isolates resistant to ≥1 ECH. Mutations were found in 44% (12/27) of isolates: 5 mutations in HS1 FKS1, 1 in HS2 FKS1, 5 in HS1 FKS2 and 1 in HS2 FKS2. Using both CAS and AFG MICs was most predictive of FKS mutations (Fig. 3).

Conclusion

ECH resistance among C. glabrata stabilized or decreased over 11-years at our hospital, in keeping with stewardship interventions to reduce prolonged use of ECHs. These results demonstrate that it is feasible to conserve ECH susceptibility.

Disclosures

Cornelius J. Clancy, MD, receives research funding paid to his institution from Astellas and Merck: Grant/Research Support|serves as an advisory Board member for Astellas, Cidara, and Scynexis, served on the advisory board for Merck, Qpex Biopharma, and Shionogi: Advisor/Consultant|Venatorx and Needham & Associates: Advisor/Consultant Minh-Hong Nguyen, MD, QPX: Grant/Research Support.

1837. Genotypic and Phenotypic Diversity of Contemporaneous Carbapenem Resistant Klebsiella pneumoniae from Blood Cultures of Individual Patients

Background

The longstanding paradigm is that almost all bloodstream infections (BSIs) stem from a single, clonal organism. We hypothesized that carbapenem resistant K. pneumoniae (CRKP) from individual patients (pts) with BSIs are genetically diverse and manifest phenotypic differences that are not typically recognized by the clinical microbiology laboratory at time of diagnosis.

Methods

We streaked blood culture (BC) broth from 6 pts with CRKP BSI onto blood agar plates, and randomly picked 9 colonies (strains) for HiSeq (Illumina) whole genome sequence. Single BSI isolates recovered by the clinical micro lab from individual pts underwent short- and long-read MinION (ONT) sequencing.

Results

2 pts were infected with clade 1 (B, G), and 4 with clade 2 (A, D, F, J) ST258 KPC-producing KP. Strains from individual pts clustered by cgSNP phylogeny (Fig. 1A-B). BC bottles from each pt harbored genetically heterogenous KP populations, with strains differing from each other by cgSNPs (Fig. 1B), presence/absence of specific antibiotic resistance genes (Fig. 1A), mutations of capsular genes (Fig 2) and at other loci involved in host interactions, and/or loss of plasmids or plasmid-borne genes (Fig. 1A). Differences in capsular gene composition were observed in KL107 capsule type strains from pts A, D and J (Fig. 2). Pangenome analyses showed accessory gene composition diversity among strains from all pts (Fig. 3). Intra-pt genetically diverse strains exhibited differences in antibiotic resistance (Fig. 4), viscosity and mucosity, capsular content, and resistance to serum and macrophage killing. Various strains from pts A and J differed in ability to cause target organ infections or mortality in a mouse model of intravenous disseminated infection (Fig. 5).

Conclusion

We identified genotypic and phenotypic variant strains of ST258 KP from BSIs of individual patients that were not recognized at time of diagnosis. Our data suggest a new, population-based paradigm for BSIs by CRKP. The findings potentially have profound implications for medical, microbiology laboratory and infection prevention practices, and for understanding emergence of antibiotic resistance and pathogenesis.

Disclosures

Cornelius J. Clancy, MD, receives research funding paid to his institution from Astellas and Merck: Grant/Research Support|serves as an advisory Board member for Astellas, Cidara, and Scynexis, served on the advisory board for Merck, Qpex Biopharma, and Shionogi: Advisor/Consultant|Venatorx and Needham & Associates: Advisor/Consultant.

Optimal ceftazidime/avibactam dosing exposure against KPC-producing Klebsiella pneumoniae

OBJECTIVES

Infections due to carbapenem-resistant Enterobacterales are considered urgent public health threats and often treated with a β-lactam/β-lactamase inhibitor combination. However, clinical treatment failure and resistance emergence have been attributed to inadequate dosing. We used a novel framework to provide insights of optimal dosing exposure of ceftazidime/avibactam.

METHODS

Seven clinical isolates of Klebsiella pneumoniae producing different KPC variants were examined. Ceftazidime susceptibility (MIC) was determined by broth dilution using escalating concentrations of avibactam. The observed MICs were characterized as response to avibactam concentrations using an inhibitory sigmoid Emax model. Using the best-fit parameter values, %fT>MICi was estimated for various dosing regimens of ceftazidime/avibactam. A hollow-fibre infection model (HFIM) was subsequently used to ascertain the effectiveness of selected regimens over 120 h. The drug exposure threshold associated with bacterial suppression was identified by recursive partitioning.

RESULTS

In all scenarios, ceftazidime MIC reductions were well characterized with increasing avibactam concentrations. In HFIM, bacterial regrowth over time correlated with emergence of resistance. Overall, suppression of bacterial regrowth was associated with %fT>MICi ≥ 76.1% (100% versus 18.2%; P < 0.001). Using our framework, the optimal drug exposure could be achieved with ceftazidime/avibactam 2.5 g every 12 h in 5 out of 7 isolates. Furthermore, ceftazidime/avibactam 2.5 g every 8 h can suppress an isolate deemed resistant based on conventional susceptibility testing method.

CONCLUSIONS

An optimal drug exposure to suppress KPC-producing bacteria was identified. The novel framework is informative and may be used to guide optimal dosing of other β-lactam/β-lactamase inhibitor combinations. Further in vivo investigations are warranted.

Cefiderocol for the Treatment of Infections Due to Metallo-B-lactamase-Producing Pathogens in the CREDIBLE-CR and APEKS-NP Phase 3 Randomized Studies

In the CREDIBLE-CR and APEKS-NP studies, cefiderocol treatment was effective against gram-negative bacteria producing metallo-B-lactamases; rates of clinical cure (70.8% [17/24]), microbiological eradication (58.3% [14/24]), and day 28 all-cause mortality (12.5% [3/24]) compared favorably with comparators of best-available therapy and high-dose meropenem (40.0% [4/10], 30.0% [3/10], and 50.0% [5/10], respectively).

Genomic characterization of lytic bacteriophages targeting genetically diverse Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa infections can be difficult to treat and new therapeutics are needed. Bacteriophage therapy is a promising alternative to traditional antibiotics, but large numbers of isolated and characterized phages are lacking. We collected 23 diverse P. aeruginosa isolates from people with cystic fibrosis (CF) and clinical infections, and used them to screen and isolate over a dozen P. aeruginosa-targeting phages from hospital wastewater. Phages were characterized with genome sequencing, comparative genomics, and lytic activity screening against all 23 bacterial host isolates. We evolved bacterial mutants that were resistant to phage infection for four different phages, and used genome sequencing and functional analysis to study them further. We also tested phages for their ability to kill P. aeruginosa grown in biofilms in vitro and ex vivo on CF airway epithelial cells. Overall, this study demonstrates how systematic genomic and phenotypic characterization can be deployed to develop bacteriophages as precision antibiotics.

Convergent Evolution of Antibiotic Tolerance in Patients with Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia

Severe infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are often complicated by persistent bacteremia (PB) despite active antibiotic therapy. Antibiotic resistance rarely contributes to MRSA-PB, suggesting an important role for antibiotic tolerance pathways. To identify bacterial factors associated with PB, we sequenced the whole genomes of 206 MRSA isolates derived from 20 patients with PB and looked for genetic signatures of adaptive within-host evolution. We found that genes involved in the tricarboxylic acid cycle (citZ and odhA) and stringent response (rel) bore repeated, independent, protein-altering mutations across multiple infections, indicative of convergent evolution. Both pathways have been linked previously to antibiotic tolerance. Mutations in citZ were identified most frequently, and further study showed they caused antibiotic tolerance through the loss of citrate synthase activity. Isolates harboring mutant alleles (citZ, odhA, and rel) were sampled at a low frequency from each patient but were detected in 10 (50%) of the patients. These results suggest that subpopulations of antibiotic-tolerant mutants emerge commonly during MRSA-PB. Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital-acquired infection. In severe cases, bacteria invade the bloodstream and cause bacteremia, a condition associated with high mortality. We analyzed the genomes of serial MRSA isolates derived from patients with bacteremia that persisted through active antibiotic therapy and found a frequent evolution of pathways leading to antibiotic tolerance. Antibiotic tolerance is distinct from antibiotic resistance, and the role of tolerance in clinical failure of antibiotic therapy is defined poorly. Our results show genetic evidence that perturbation of specific metabolic pathways plays an important role in the ability of MRSA to evade antibiotics during severe infection.

Mechanisms of Reduced Susceptibility to Cefiderocol Among Isolates from the CREDIBLE-CR and APEKS-NP Clinical Trials

The objective of this study was to characterize isolates with reduced susceptibility to cefiderocol in patients receiving cefiderocol for nosocomial pneumonia or carbapenem-resistant infections in the Phase 3 APEKS-NP and CREDIBLE-CR studies. Susceptibility testing of isolates was conducted at a central laboratory, and post-treatment changes were evaluated according to available breakpoints for cefiderocol. Whole-genome sequencing and multilocus sequence typing were performed for isolates to confirm their origin and identify mutations. Five (APEKS-NP) and nine (CREDIBLE-CR) isolates demonstrated a ≥ 4-fold minimum inhibitory concentration (MIC) increase compared with genetically related baseline isolates; most remained susceptible to cefiderocol despite the ≥4-fold MIC increase. Mutations in β-lactamases or penicillin-binding protein (PBP) were identified in 4/14 isolates: one Enterobacter cloacae (amino acid [AA] substitution [A313P] in ACT-17); two Acinetobacter baumannii (one PBP3 AA substitution [H370Y], one with OXA-23 substitutions [N85I and P225S]); and one Pseudomonas aeruginosa (PDC-30 [4AA deletion "TPMA" position 316-319]). Cloning experiments using isogenic Escherichia coli strains containing wild-type and those mutant cephalosporinase enzymes show that the mutant enzymes may contribute to decreased susceptibility to cefiderocol. Pharmacokinetic data were available for nine patients, for whom cefiderocol exposures exceeded 100% fT > 4 × MIC. No clear pattern between mutations and development or extent of MIC increases was observed. No mutations were identified in genes related to iron transport, including fiu, cirA, piuA/C, and pirA, among recovered Gram-negative isolates. Clinicaltrials.gov: APEKS-NP: NCT03032380; CREDIBLE-CR: NCT02714595.

Isolation and Characterization of Lytic Bacteriophages Targeting Diverse Enterobacter spp. Clinical Isolates

Background: Enterobacter spp. are opportunistic pathogens that cause nosocomial infections. Bacteriophages could be used to treat antibiotic-resistant Enterobacter infections. Materials and Methods: We used 10 genetically diverse clinical Enterobacter spp. isolates to identify lytic bacteriophages in hospital and municipal wastewater. Comparative genomics was performed on host bacterial isolates and isolated phages. Activity of each phage against all 10 host isolates was determined. We also tested phage activity against paired isolates from two patients who developed ceftazidime-avibactam resistance. Results: Bacteria belonged to three Enterobacter species and Klebsiella aerogenes. We isolated 12 bacteriophages, most of which belonged to the Myoviridae and Autographiviridae families. Most phages were able to lyse multiple bacterial isolates, and many lysed isolates of different species. Ceftazidime-avibactam-resistant isolates were still phage susceptible, and one isolate showed increased susceptibility compared with the parent isolate. Conclusion: The phages we isolated expand the diversity of Enterobacter-targeting phages, and could be useful for treating antibiotic-resistant Enterobacter infections.

Evolution of Imipenem-Relebactam Resistance Following Treatment of Multidrug-Resistant Pseudomonas aeruginosa Pneumonia

We report the emergence of imipenem-relebactam nonsusceptible Pseudomonas aeruginosa in 5 patients treated for nosocomial pneumonia for 10-28 days. Genome sequence analysis identified treatment-emergent mutations in MexAB-OprM and/or MexEF-OprN efflux operons that arose independently in each patient across distinct P. aeruginosa sequence types. Testing with efflux-inhibitor PAβN restored imipenem-relebactam susceptibility.

In Vitro Evolution of Cefiderocol Resistance in an NDM-Producing Klebsiella pneumoniae Due to Functional Loss of CirA

By serially exposing an NDM-producing Klebsiella pneumoniae clinical strain to cefiderocol, we obtained a mutant with cefiderocol MIC of >128 μg/ml. The mutant contained an early stop codon in the iron transporter gene cirA, and its complementation fully restored susceptibility. The cirA-deficient mutant was competed out by the parental strain in vitro, suggesting reduced fitness. IMPORTANCE Cefiderocol, a newly approved cephalosporin agent with an extensive spectrum of activity against Gram-negative bacteria, is a siderophore cephalosporin that utilizes iron transporters to access the bacterial periplasm. Loss of functional CirA, an iron transporter, has been associated with cefiderocol resistance. Here, we show that such genetic change can be selected under selective pressure and cause high-level cefiderocol resistance, but with a high fitness cost. Whether these resistant mutants can survive beyond selective pressure will inform stewardship of this agent in the clinic.

Changing Epidemiology and Decreased Mortality Associated With Carbapenem-resistant Gram-negative Bacteria, 2000-2017

BACKGROUND

Carbapenem-resistant gram-negative bacteria (CRGNB) continue to present a global healthcare crisis. We aimed to identify emerging trends of CRGNB over nearly 2 decades and describe the impact of CRGNB on patient outcomes.

METHODS

Patients from whom CRGNB were isolated between 2000 and 2017 were included in the study. Carbapenem resistance was defined by the most recent breakpoints and applied across the study period. Patient demographics, clinical characteristics, and outcomes were retrieved from the electronic health record.

RESULTS

A total of 94 888 isolates from 64 422 patients were identified; 9882 (10%) isolates from 4038 patients were carbapenem-resistant. Pseudomonas aeruginosa was the most common CRGNB each year. The second most common CRGNB emerged in waves over time. Carbapenem daily defined doses increased in parallel with CRGNB rates (R2 = 0.8131). The overall 30-day mortality rate was 19%, which decreased from 24% in 2000 to 17% in 2017 (P = .003; R2 = .4330). Among patients with CRGNB bloodstream infections (n = 319), overall 30- and 90-day mortality rates were 27% and 38%, respectively. Charlson score (adjusted odds ratio [aOR], 1.11 per point), intensive care unit residence (aOR, 7.32), and severe liver disease (aOR, 4.8.4) were independent predictors of 30-day mortality, while receipt of transplantation was associated with lower rates of death (aOR, 0.39). Among patients admitted between 2011 and 2017 (n = 2230), 17% died during hospitalization, 32% were transferred to long-term care facilities, and 38% were discharged home.

CONCLUSIONS

CRGNB emerged in waves over time, causing high rates of mortality. Despite increasing rates of CRGNB, overall patient outcomes have improved, suggesting that recognition and novel therapeutics have made a major impact.

654. Performance of the T2Resistance Panel in Detecting Antibiotic Resistant Bacteria Directly in Whole Blood, and Implications for Improving Appropriate Therapy of Bloodstream Infections

Background

Appropriate antibiotic (Ab) therapy of bloodstream infections (BSI) is often delayed by time to blood culture (BC) positivity, species (sp) identification and Ab sensitivity (sensi). The T2Resistance (T2R) Panel is a direct-from-blood (culture-independent) diagnostic that detects 13 genetic markers associated with methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococcus (VRE), ESBL- and carbapenemase-producing Enterobacteriaceae (E). We assessed T2R performance in detecting these resistant bacteria in whole blood (WB) and analyzed possible impact on time to appropriate Ab.

Methods

We performed T2R using WB samples obtained from patients (pts) on the same day as BCs from July 2019-2020. Receipt of appropriate Ab was assessed at time of empiric, Gram stain-directed, MALDI-directed (sp identification) and sensi-directed therapy. T2R results were not available to care teams. Teams were notified of positive BCs. Stewardship optimized Abs based on sensi.

Results

BC from 103 pts grew 114 bacterial sp: E (n=54; 16 ESBL-, 1 KPC-producer), S. aureus (n=29, 22 MRSA), Enterococcus (n=21, 16 VRE), P. aeruginosa and others (n=10). 12 ESBL-E produced CTX-M 14/15. T2R sensitivity and specificity was 78% and 99%, respectively, compared to sequencing of resistance markers. Sensitivity was excellent for vanA/B, KPC (100% each), and CTX-M14/15 (92%); sensitivity was 58% for mecA/C. T2R detected resistance determinants in 3-7h. Median time to appropriate Ab was 16.3h, which was significantly longer for VRE (25.6h) and ESBL- or KPC-E (50.9h) BSIs than for T2R marker-negative bacteria (6.7h; p=0.04). Pts with VRE or ESBL-/KPC-E BSI were less likely to received appropriate empiric Ab (18% and 30%, respectively) than pts with T2R marker-negative BSI (63%; p=0.02; Fig.1). Median times to achieve ≥80% appropriate Ab therapy of marker-negative, VRE and CTX-M/KPC-E BSIs were 15.5h (after Gram stain), 43.9h (after MALDI) and 63.5h (after sensi), respectively.

Antibiotic Therapy

Conclusion

There was a significant delay in appropriate Ab therapy of BSIs, especially in pts infected with VRE and ESBL/KPC-E. T2R rapidly and accurately detected BSI caused by VRE and ESBL/KPC-E, and has the potential to significantly shorten time to appropriate Ab.

Disclosures

Cornelius J. Clancy, MD, Merck (Grant/Research Support) Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) Minh-Hong Nguyen, MD, Merck (Grant/Research Support)

1276. Assessment of Anti-biofilm Activity of Staphylococcus aureus Bacteriophages Against Clinical Isolates from Patients with Left Ventricular Assist Device Infections

Background

Staphylococcus aureus is a common cause of biofilm-mediated left ventricular device (LVAD) infections which are difficult to resolve with antibiotics alone and are associated with substantial morbidity and mortality. Recently, bacteriophages (phage) therapy has been used to resolve LVAD infections in a few cases. Our goal was to assess in vitro susceptibility and anti-biofilm activity of two S. aureus bacteriophages against clinical isolates from patients with S. aureus LVAD infections in order to develop a S. aureus phage cocktail for clinical use.

Methods

Two bacteriophages, OMS1 and OMS2, from the Israeli Phage Bank, were assessed for lytic activity against 15 S.aureus isolates (9 methicillin resistant, MRSA and 6 methicillin susceptible, MSSA) via agar overlay method and plaque forming units (PFU)/mL were enumerated. We then formed bacterial biofilms after overnight incubation at 120 rpm in a 96-well plates in duplicate; experiments were repeated thrice. Wells were then treated with tryptic soy broth (TSB, control) or TSB containing phage at 109 PFU/mL for 24 hours. After washing, biofilms were stained with crystal violet and biomass quantified via optical density at 570mm.

Results

All bacterial isolates were susceptible to both phages via agar overlay to varying degrees as determined by phage titers obtained via serial dilutions (Figure 1a, 1b). OMS1 led to significant reduction in biofilm of 7/9 MRSA and 3/6 MSSA isolates and OMS2 reduced biofilms in 9/9 MRSA and 4/6 MSSA isolates (Figure 1c).

Phage titers and Biofilm Biomass

Conclusion

We demonstrated in vitro lytic and anti-biofilm activity of 2 S. aureus phages against clinical S. aureus isolates from patients with LVAD infection. Our data suggests that phage susceptibility measured with agar overlay does not always correlate with phage susceptibility of S. aureus biofilms, suggesting that more than one method should be used to assess in vitro activity. We plan to assess for synergistic activity with the phage combination.

Disclosures

Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) Ran Nir-Paz, MD, BiomX (Consultant)Technophage (Scientific Research Study Investigator, Advisor or Review Panel member) Saima Aslam, MD, MS, BioMx (Consultant)Cystic Fibrosis Foundation (Grant/Research Support)Gilead (Consultant)Johnson and Johnson (Consultant)Merck (Consultant)

1100. A Prospective Evaluation of Neurotoxicity Among Patients Receiving Dose-Optimized Cefepime or Meropenem With Concomitant Therapeutic Drug Monitoring

Background

Cefepime (FEP) induced neurotoxicity (NT) may have serious implications for patients (pts). Retrospective studies have employed variable definitions of NT, finding renal impairment and FEP trough concentrations (Cmin) > 20 mg/L as risk factors. Prospective studies comparing antibiotics have not been performed.

Methods

We conducted a prospective study of pts receiving FEP or meropenem (MEM) with neurologic evaluation and therapeutic drug monitoring (TDM). A NT advisory board (NTAB) was established to develop standardized definitions of possible, probable and definitive NT (Fig 1). Cases of potential NT were adjudicated by the NTAB who were blinded to study treatment. FEP and MEM midpoint and Cmin concentrations were measured at steady-state by validated methods.

Results

127 patients were included (70 FEP, 57 MEM). Demographics and treatment characteristics were similar between groups (Fig 2); 63% were in the ICU. FEP and MEM Cmin varied from 1.9 – 140.5 and 0.6 – 31.3 mg/L, respectively. Median FEP Cmin and total exposures (AUC) were 23.1 mg/L and 347.6 hr*mg/L, respectively. Corresponding MEM values were 5.9 mg/L and 124.8 hr*mg/L, respectively. Cmin values were inversely correlated with renal function for both FEP and MEM (P< 0.001). Rates of possible, probable, or definitive NT were 10% and 5% for FEP and MEM, respectively (P=0.51; Fig 3). 16% and 3% of pts with FEP Cmin > or < 20 mg/L had NT, respectively (P=0.11; Fig 4). Median MEM Cmin were 12.3 and 5.4 mg/L among pts with and without NT, respectively (P=0.09; Fig 4). Rates of NT did not vary by infusion length or dose. FEP and MEM exposures were similar between patients with (17%) or without (83%) microbiologic recurrence due to the same pathogen. FEP was discontinued in 4 pts due to NT; no pts stopped MEM due to NT.

Conclusion

Our study is the first to evaluate FEP NT prospectively and compare rates of NT to pts receiving MEM. We established criteria that were applied by a blinded NTAB. In doing so we found rates of NT to be lower than previously reported and not statistically different between FEP and MEM. Cmin values were highly variable and associated with numerically, but not statistically higher rates of NT for both agents. These findings serve as the basis for larger, multicenter studies and justify use of routine TDM to limit NT among high-risk pts.

Disclosures

Brandon Smith, MD, PharmD, Shionogi (Consultant, Advisor or Review Panel member) Alexandra Urban, MD, Neuropace (Consultant) Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support)

308. Secondary Infections in Patients Requiring Extracorporeal Membrane Oxygenation (ECMO) for Severe Acute Respiratory Distress Syndrome (ARDS) due to COVID-19 Pneumonia (PNA)

Background

Rescue ECMO has been used worldwide in patients (pts) with ARDS caused by COVID-19. Bacterial super-infections affect 3.5-14.3% of hospitalized pts with COVID-19. Pts requiring ECMO may be at an increased risk of infection due to their severity of illness, gut translocation and ECMO impact on host immunity.

Methods

This was a retrospective review of pts requiring ECMO for COVID-19 from April 2020-2021 at a single center. Strict definitions of infections (including ventilator-associated PNA, VAP) were in accordance with CDC criteria.

Results

43 ECMO pts with 1065 ECMO days were evaluated. Median age was 53 yrs (range: 21-62) and median BMI was 36.2 (range: 19.4-75.8). 70% were men and 65% were white. 37 patients (86%) experienced a total of 40 infectious episodes with a median onset from ECMO cannulation to first infection of 10.5d (range: 4-50). Median SOFA and SAPSII scores at time of infection were 12 (6-20) and 63 (30-90), respectively. PNA was the most common infection (78%, with 19% of cases complicated by bacteremia and 3% by empyema) (Fig. 1). The most common organisms isolated were Enterobacterales (37%), S. aureus (25%) and P. aeruginosa (16%) (Fig. 2). Only 2% of all organisms were multi-drug resistant. 3 pts had fungal infections (1 candidemia, 2 aspergillus PNA). Duration of ECMO was significantly longer for infected pts (26d, range: 5-92d) vs (11d, range: 3-24d), p=.01. 95% of infected pts had received steroids vs. 67% of uninfected pts, p=0.09. Treatment success at 1 week was 50%, and 24% and 40% of pts had recurrent infections and persistent/recurrent organisms in clinical cultures, respectively. S. aureus (54%) and Enterobacterales (26%) were associated with persistent or recurrent clinical cultures, requiring prolonged antimicrobial therapy. Mortality rate at 30 days was 65% and was significantly higher for pts with infection than those without (67% vs 33%, p=.02).

Conclusion

Super-infection (most commonly PNA) occurred in almost all COVID-19 pts requiring ECMO for &gt;4 days, and was a significant risk factor for death. Recurrent infections among survivors were common, especially when caused by Enterbacterales or S. aureus. Super-infection and mortality rates of ARDS pts on ECMO for COVID-19 were worse than for ARDS pts on ECMO for influenza at our center.

Disclosures

Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) Fernanda P. Silveira, MD, MS, FIDSA, Ansun (Individual(s) Involved: Self): Grant/Research Support; Novartis (Individual(s) Involved: Self): Grant/Research Support; Qiagen (Individual(s) Involved: Self): Grant/Research Support; Shire (Individual(s) Involved: Self): Advisor or Review Panel member, Grant/Research Support; SlieaGen (Individual(s) Involved: Self): Grant/Research Support; Whiscon (Individual(s) Involved: Self): Grant/Research Support Cornelius J. Clancy, MD, Merck (Grant/Research Support)