Rapid Molecular Diagnostics to Inform Empiric Use of Ceftazidime/Avibactam and Ceftolozane/Tazobactam Against Pseudomonas aeruginosa: PRIMERS IV

BACKGROUND

Overcoming β-lactam resistance in pathogens such as Pseudomonas aeruginosa is a major clinical challenge. Rapid molecular diagnostics (RMDs) have the potential to inform selection of empiric therapy in patients infected by P. aeruginosa.

METHODS

In this study, we used a heterogeneous collection of 197 P. aeruginosa that included multidrug-resistant isolates to determine whether 2 representative RMDs (Acuitas Resistome test and VERIGENE gram-negative blood culture test) could identify susceptibility to 2 newer β-lactam/β-lactamase inhibitor (BL-BLI) combinations, ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (TOL/TAZO).

RESULTS

We found that the studied RMD platforms were able to correctly identify BL-BLI susceptibility (susceptibility sensitivity, 100%; 95% confidence interval [CI], 97%, 100%) for both BLs-BLIs. However, their ability to detect resistance to these BLs-BLIs was lower (resistance sensitivity, 66%; 95% CI, 52%, 78% for TOL/TAZO and 33%; 95% CI, 20%, 49% for CZA).

CONCLUSIONS

The diagnostic platforms studied showed the most potential in scenarios where a resistance gene was detected or in scenarios where a resistance gene was not detected and the prevalence of resistance to TOL/TAZO or CZA is known to be low. Clinicians need to be mindful of the benefits and risks that result from empiric treatment decisions that are based on resistance gene detection in P. aeruginosa, acknowledging that such decisions are impacted by the prevalence of resistance, which varies temporally and geographically.

Predicting β-lactam resistance using whole genome sequencing in Klebsiella pneumoniae: the challenge of β-lactamase inhibitors

Although multiple antimicrobial resistance (AMR) determinants can confer the same in vitro antimicrobial susceptibility testing (AST) phenotype, their differing effect on optimal therapeutic choices is uncertain. Using a large population-based collection of clinical strains spanning a 3.5-year period, we applied WGS to detect inhibitor resistant (IR), extended-spectrum β-lactamase (ESBL), and carbapenem resistant (CR) β-lactamase (bla) genes and compared the genotype to the AST phenotype in select isolates. All bla_NDM-1 (9/9) and the majority of bla_NDM-1/OXA-48 (3/4) containing isolates were resistant to CAZ/AVI as predicted by WGS. The combination of ATM and CAZ/AVI restored susceptibility by disk diffusion assay. Unexpectedly, clinical Kp isolates bearing bla_KPC-8 (V240G) and bla_KPC-14 (G242 and T243 deletion) did not test fully resistant to CAZ/AVI. Lastly, despite the complexity of the β-lactamase background, CAZ/AVI retained potency. Presumed phenotypes conferred by AMR determinants need to be tested if therapeutic decisions are being guided by their presence or absence.

A γ-Lactam Siderophore Antibiotic Effective against Multidrug-Resistant Gram-Negative Bacilli

Treatment of multidrug-resistant Gram-negative bacterial pathogens represents a critical clinical need. Here, we report a novel γ-lactam pyrazolidinone that targets penicillin-binding proteins (PBPs) and incorporates a siderophore moiety to facilitate uptake into the periplasm. The MIC values of γ-lactam YU253434, 1, are reported along with the finding that 1 is resistant to hydrolysis by all four classes of β-lactamases. The druglike characteristics and mouse PK data are described along with the X-ray crystal structure of 1 binding to its target PBP3.

Molecular and clinical epidemiology of carbapenem-resistant Enterobacterales in the USA (CRACKLE-2): a prospective cohort study

BACKGROUND

Carbapenem-resistant Enterobacterales (CRE) are a global threat. We aimed to describe the clinical and molecular characteristics of Centers for Disease Control and Prevention (CDC)-defined CRE in the USA.

METHODS

CRACKLE-2 is a prospective, multicentre, cohort study. Patients hospitalised in 49 US hospitals, with clinical cultures positive for CDC-defined CRE between April 30, 2016, and Aug 31, 2017, were included. There was no age exclusion. The primary outcome was desirability of outcome ranking (DOOR) at 30 days after index culture. Clinical data and bacteria were collected, and whole genome sequencing was done. This trial is registered with ClinicalTrials.gov, number NCT03646227.

FINDINGS

1040 patients with unique isolates were included, 449 (43%) with infection and 591 (57%) with colonisation. The CDC-defined CRE admission rate was 57 per 100 000 admissions (95% CI 45-71). Three subsets of CDC-defined CRE were identified: carbapenemase-producing Enterobacterales (618 [59%] of 1040), non-carbapenemase-producing Enterobacterales (194 [19%]), and unconfirmed CRE (228 [22%]; initially reported as CRE, but susceptible to carbapenems in two central laboratories). Klebsiella pneumoniae carbapenemase-producing clonal group 258 K pneumoniae was the most common carbapenemase-producing Enterobacterales. In 449 patients with CDC-defined CRE infections, DOOR outcomes were not significantly different in patients with carbapenemase-producing Enterobacterales, non-carbapenemase-producing Enterobacterales, and unconfirmed CRE. At 30 days 107 (24%, 95% CI 20-28) of these patients had died.

INTERPRETATION

Among patients with CDC-defined CRE, similar outcomes were observed among three subgroups, including the novel unconfirmed CRE group. CDC-defined CRE represent diverse bacteria, whose spread might not respond to interventions directed to carbapenemase-producing Enterobacterales.

FUNDING

National Institutes of Health.

Core genome MLST and resistome analysis of Klebsiella pneumoniae using a clinically amenable workflow

Whole genome sequencing (WGS) is replacing traditional microbiological typing methods for investigation of outbreaks in clinical settings. Here, we used a clinical microbiology laboratory core genome multilocus sequence typing (cgMLST) workflow to analyze 40 isolates of K. pneumoniae which are part of the Antimicrobial Resistance Leadership Group (ARLG) isolate collection, alongside 10 Mayo Clinic K. pneumoniae isolates, comparing results to those of pulsed-field gel electrophoresis (PFGE). Additionally, we used the WGS data to predict phenotypic antimicrobial susceptibility (AST). Thirty-one of 40 ARLG K. pneumoniae isolates belonged to the same PFGE type, all of which, alongside 3 isolates of different PFGE types, formed a large cluster by cgMLST. PFGE and cgMLST were completely concordant for the 10 Mayo Clinic K. pneumoniae isolates. For AST prediction, the overall agreement between phenotypic AST and genotypic prediction was 95.6%.

698. In vitro Activity of a New Generation Oxopyrazole Antibiotic Against Multidrug-Resistant Gram-Negative Bacilli

Background

Multidrug-resistant Gram-negative bacilli (MDRGNB) are emerging as a challenging cause of hospital-acquired infections and represent a critical need for innovative antibacterial development. New oxopyrazole agents targeting penicillin-binding proteins (PBPs) based on a non-β-lactam core and incorporating a siderophore moiety (Figure 1) which facilitates transport to the periplasm are being developed that show promise against Gram-negative organisms including multidrug-resistant strains of E. coli, K. pneumoniae and P. aeruginosa.

Methods

YU253434, an example of this new class of antibacterials, was investigated in vitro. Minimum inhibitory concentrations (MICs) were determined by broth microdilution against a representative panel comprising 15 strains each of E. coli, K. pneumoniae and P. aeruginosa, which contain extended-spectrum β-lactamase (ESBL) and/or carbapenemases genes.All studies were performed according to current Clinical & Laboratory Standards Institute (CLSI) guidelines using iron-depleted media. Ceftazidime breakpoints were arbitrability chosen as a reference for YU253434 (susceptibilities ≤4 μg/mL for Enterobacteriaceae and ≤8 μg/mL for P. aeruginosa).

Results

MIC testing (Figures 2–4) against E. coli showed 11 strains were YU253434 susceptible (compared with 6 for ceftazidime, and 3 for imipenem); against K. pneumoniae 13 strains were YU253434 susceptible (compared with 2 for ceftazidime and 6 for imipenem); against P. aeruginosa 10 strains were YU253434 susceptible (compared with 0 for both ceftazidime and imipenem). There appeared to be no correlation between YU253434 resistance and the presence of specific lactamase genes.

Conclusion

YU253434, a new generation oxopyrazole antibiotic, demonstrated promising in vitro potency against a panel of E. coli, K. pneumonia, and P. aeruginosa strains which contain ESBL and/or carbapenemases genes.

Disclosures

All authors: No reported disclosures.

687. In vitro Activity of a New Generation Oxopyrazole Antibiotic Against Acinetobacter spp

Background

Acinetobacter spp. resistant to common antibiotics have become a worrying cause of hospital-acquired infections and represent a critical need for innovative antibacterial development. New oxopyrazole agents targeting penicillin-binding proteins (PBPs) based on a non-β-lactam core and incorporating a siderophore moiety (figure) which facilitates transport to the periplasm are being developed which show promise against Gram-negative organisms including Acinetobacter spp.

Methods

YU253911, an example of this new class of antibacterials, was characterized in vitro. Minimum inhibitory concentrations (MICs) were determined by broth microdilution against a collection of 200 previously described (whole-genome sequencing) Acinetobacter isolates including 98 carbapenem-resistant A. baumannii strains. YU253911’s antimicrobial activity was also evaluated in combination with complementary PBP agents and β-lactamase inhibitors by MIC and disc diffusion testing. All studies were performed according to current Clinical and Laboratory Standards Institute (CLSI) guidelines using iron-depleted media. Breakpoints for ceftazidime were arbitrarily chosen as reference.

Results

Using ceftazidime (breakpoint ≤8 μg/mL) as a comparator, 175 of the 200 Acinetobacter isolates were susceptible to YU253911, which possessed an MIC₅₀ of 0.5 μg/mL and an MIC₉₀ of 16 μg/mL. This compared favorably to all previously tested β-lactams including penicillins, cephalosporins, monobactams and carbapenems (MIC₅₀s 2 to >16 μg/mL). Against the subset of carbapenem-resistant A. baumannii isolates, YU253911’s potency was similar with an MIC₅₀ of 1 μg/mL. Genetic analysis showed β-lactamase genes, including OXA-23 and other carbapenemases, were common in both YU253911-resistant and susceptible strains.

Conclusion

YU253911 demonstrates promising in vitro potency against a collection of Acinetobacter isolates and compares favorably to β-lactam antibiotics. Understanding interactions with PBP agents and β lactamase inhibitors is being explored as well as further studies on the mechanism of resistance.

Disclosures

All authors: No reported disclosures.

609. Differing Genotypic Contexts Between E. coli and A. baumannii Modulate the Role of blaADC-7 in the Development of Antibiotic Collateral Sensitivity

Background

Antibiotic resistance is a global health crisis. While persistent drug discovery of novel antibiotics has previously been relied upon to thwart resistance, evolution inevitably perseveres. While genes conferring antibiotic resistance have previously been characterized, it is unclear how varying genetic contexts can change the antibiotic resistance phenotype a given gene confers.

Methods

The DH10B strain of E. coli was transformed with a blaADC-7 plasmid. In 12 evolutionary replicates, the modified E. coli strain and a clinical strain of A. baumannii containing the same resistance gene were passaged daily for 10 days on cefepime gradient agar plates with gradually increasing concentrations of cefepime. MICs of cefepime and a diverse set of 15 other drugs were determined for the parental strains and after the final passage passage. MIC of cefepime after intermediary passages were determined for select replicates. Lastly the blaADC-7 gene after the final passage was sequenced.

Results

At the end of 10 passages, collateral sensitivity in A. baumannii was observed to tigecycline and fosfomycin in 5 and 6 replicates respectively, out of 12 total. 4 out of 12 E. coli replicates displayed collateral sensitivity to minocycline (Figure 1). In the third E. coli replicate, Sanger sequencing revealed a novel S286R mutation in blaADC-7 appearing in passage seven which preceded a several log fold increase in the MIC of cefepime (Figures 2 and 3). No additional mutations were found in the other evolutionary replicates.

Conclusion

Patterns of resistance varied among antibiotics of the same class, (e.g., tetracyclines, fourth-generation cephalosporins) in both E. coli and A. baumannii; however, A. baumannii expressed less widespread collateral resistance than E. coli. A previously undiscovered S286R mutation in blaADC-7 coincided with a pronounced increased in resistance to cefepime. Further studies are required to determine whether this mutation gives rise to a structural change in the protein product. Given that no other mutations were found, resistance to cefepime and subsequent collateral resistance to other antibiotics may have developed due to epigenetic changes or mutations outside the blaADC-7 genes. Indeed, future experiments with whole-genome sequencing may reveal such changes.

Disclosures

All authors: No reported disclosures.

The Clinical and Molecular Epidemiology of CTX-M-9 Group Producing Enterobacteriaceae Infections in Children

Introduction

The pandemic of extended-spectrum beta-lactamase-(ESBL)-producing Enterobacteriaceae (Ent) is strongly linked to the dissemination of CTX-M-type-ESBL-Ent. We sought to define the epidemiology of infections in children due to an emerging resistance type, CTX-M-9-group-producing-Ent (CTX-M-9-grp-Ent).

Methods

A retrospective matched case-control analysis of children with CTX-M-9-grp-Ent infections who received medical care at three Chicago area hospitals was performed. Cases were defined as children possessing extended-spectrum cephalosporin-resistant (ESC-R) infections due to bla_CTX-M-9. PCR and DNA analysis assessed beta-lactamase (bla) genes, multi-locus sequence types (MLST) and phylogenetic grouping of E. coli. Controls were children with ESC-susceptible (ESC-S)-Ent infections matched one case to three controls by age, source, and hospital. The clinical-epidemiologic predictors of CTX-M-9-grp-Ent infection were assessed.

Results

Of 356 ESC-R-Ent isolates from children (median age 4.1 years), the CTX-M-9-group was the solely detected bla gene in 44 (12.4%). The predominant species was E. coli (91%) of virulent phylogroups D (60%) and B2 (40%). MLST revealed multiple strain types. On multivariable analysis, CTX-M-9-grp-Ent occurred more often in E. coli than other Ent genera (OR 7.4, 95% CI 2.4, 27.2), children of non-Black-White-Hispanic race (OR 7.4, 95% CI 2.4, 28.2), and outpatients (OR 4.5, 95% CI 1.7, 12.3), which was a very unexpected finding for infections due to antibiotic-resistant bacteria. Residents of South Chicago had a 6.7 times higher odds of having CTX-M-9-grp-Ent infections than those in the reference region (West), while residence in Northwestern Chicago was associated with an 81% decreased odds of infection. Other demographic, comorbidity, invasive-device, and antibiotic use differences were not found.

Conclusion

CTX-M-9-grp-Ent infection may be associated with patient residence and is occurring in children without traditional in-patient exposure risk factors. This suggests that among children, the community environment may be a key contributor in the spread of these resistant pathogens.

ARGONAUT-I: Activity of Cefiderocol (S-649266), a Siderophore Cephalosporin, against Gram-Negative Bacteria, Including Carbapenem-Resistant Nonfermenters and Enterobacteriaceae with Defined Extended-Spectrum β-Lactamases and Carbapenemases

The activity of the siderophore cephalosporin cefiderocol is targeted against carbapenem-resistant Gram-negative bacteria. In this study, the activity of cefiderocol against characterized carbapenem-resistant Acinetobacter baumannii complex, Stenotrophomonas maltophilia, Pseudomonas aeruginosa, and Enterobacteriaceae strains was determined by microdilution in iron-depleted Mueller-Hinton broth. The MIC90s against A. baumannii, S. maltophilia, and P. aeruginosa were 1, 0.25, and 0.5 mg/liter, respectively. Against Enterobacteriaceae, the MIC90 was 1 mg/liter for the group harboring OXA-48-like, 2 mg/liter for the group harboring KPC-3, and 8 mg/liter for the group harboring TEM/SHV ESBL, NDM, and KPC-2.

The Role of Trimethoprim/Sulfamethoxazole in the Treatment of Infections Caused by Carbapenem-Resistant Enterobacteriaceae

In the Consortium on Resistance Against Carbapenems in Klebsiella and other Enterobacteriaceae (CRACKLE), trimethoprim-sulfamethoxazole (TMP-SMX) had a limited role in the treatment of less severe carbapenem-resistant Enterobacteriaceae (CRE) infections, especially urinary tract infections. Of tested CRE, only 29% were susceptible to TMP-SMX. Development of resistance further limits the use of TMP-SMX in CRE infections.

1351. In vitro Activity of Cefiderocol (S-649266), a Siderophore Cephalosporin, Against Enterobacteriaceae With Defined Extended-Spectrum Β-Lactamases and Carbapenemases

Background

Cefiderocol is a novel siderophore cephalosporin targeted for activity against carbapenem and multidrug-resistant Gram-negative species, including extended-spectrum β-lactamase (ESBL) and carbapenemase-producing strains. The Consortium on Resistance Against Carbapenems in Klebsiella and other Enterobacteriaceae (CRACKLE) is a federally funded, prospective multi-center consortium of 20 hospitals from nine US healthcare systems to track carbapenem-resistant Enterobacteriaceae.

Methods

Minimum inhibitory concentrations (MICs) of cefiderocol and meropenem were determined by broth microdilution according to current CLSI guidelines. Cefiderocol was tested in iron-depleted cation-adjusted Mueller–Hinton (MH) broth, meropenem was tested in cation-adjusted MH broth. Cefiderocol MICs were read as the first drug well in which the growth was significantly reduced (i.e., a button of <1 mm or light/faint turbidity) relative to the growth observed in the growth control well containing the same medium. Trailing endpoints were disregarded. Isolates tested included 35 Escherichia coli, five Enterobacter/Citrobacter group, and 794 Klebsiella pneumoniae. Isolates had characterized β-lactamases including TEM, SHV, and CTX-M ESBLs and KPC, NDM, and OXA carbapenemases.

Results

Cefiderocol MICs ranged from ≤0.03 to >64 mg/L, with overall MIC50 of 0.5 mg/L and MIC90 of 4 mg/L (table). MIC90 value (≤0.03 mg/L) was lowest against isolates with no ESBLs or carbapenemases. MIC90 was 1 mg/L for OXA and TEM/SHV groups, 2–4 mg/L for KPC-3 groups and 8 mg/L for NDM and KPC-2 groups.

Conclusion

Compared with isolates without ESBLs and carbapenemases, cefiderocol shows higher MICs against isolates with ESBLs, including TEM, SHV, and CTX-M and carbapenemases including KPC, NDM, and OXA. The clinical utility of cefiderocol against ESBL and carbapenemase-producing Enterobacteriaceae is dependent on the pharmacokinetic and pharmacodynamic properties of cefiderocol.

Disclosures

M. R. Jacobs, Achaogen: Investigator, Research grant. Shionogi: Investigator, Research grant. S. S. Richter, bioMerieux: Grant Investigator, Research grant. BD Diagnostics: Grant Investigator, Research grant. Roche: Grant Investigator, Research grant. Hologic: Grant Investigator, Research grant. Diasorin: Grant Investigator, Research grant. Accelerate: Grant Investigator, Research grant. Biofire: Grant Investigator, Research grant. D. Van Duin, Shionogi: Scientific Advisor, Consulting fee. achaogen: Scientific Advisor, Consulting fee. Allergan: Scientific Advisor, Consulting fee. Astellas: Scientific Advisor, Consulting fee. Neumedicine: Consultant, Consulting fee. T2 Biosystems: Scientific Advisor, Consulting fee. Roche: Scientific Advisor, Consulting fee.

1348. In vitro Activity of Plazomicin, a Next-Generation Aminoglycoside, Against Carbapenemase-Producing Klebsiella pneumoniae

Background

Methods

Results

Conclusion

Disclosures

2336. Resistance Mechanisms and Factors Associated With CTX-M-9 Group Extended-Spectrum β-Lactamase (ESBL)-Producing Enterobacteriaceae Infections in Children

Background

There is an increasing incidence of extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae infections in children. However, most studies focus only on CTX-M-1 group (CTX-M-15). We sought to define the epidemiology of the CTX-M-9 group (CTX-M-9) producing Enterobacteriaceae infections in children to devise more effective treatment and prevention strategies.

Methods

A case–control study of children (0–21 y), cared for by 3 Chicago area hospitals during 2011–16, was performed. Cases were 44 children diagnosed with third-generation cephalosporin (3GC) resistant and/or carbapenem-resistant (CR) Enterobacteriaceae infections who had CTX-M-9 genes accounting for β-lactam resistance. PCR amplification, DNA sequencing, and DNA microarray analysis (Check-Points®) assessed for bla genes. MLST, rep-PCR and phylogenetic analysis were also performed. Controls were 135 children with 3GC and carbapenem susceptible Enterobacteriaceae infections matched by age range and hospital. Demographics; comorbidities; device, antibiotic, and healthcare exposures; and the impact of location of patient residence were evaluated. Race categories were white, black, Hispanic, and other. Stratified analysis and multivariable logistic regression were used to explore associations between predictors and CTX-M-9 infection. Data were analyzed in SAS 9.4.

Results

The median age of cases was 4.1 years. The predominant organism (39/44, 89%) was E. coli of virulent phylogroups B2 (41%) and D (59%). MLST analysis revealed that this collection of strains was polyclonal.

On multivariable analysis, children with CTX-M-9 Enterobacteriaceae infections were more likely to be diagnosed in an outpatient clinic (OR 4.5), have E. coli infection (OR 7.0), and be of race “other” (OR 7.6) vs. controls. Residents of South Chicago were 6.7 times more likely to have a CTX-M-9 Enterobacteriaceae infection than controls; while residence in Northwest Chicago was associated with a 81% decreased risk. Significant differences in other demographics, comorbidities, invasive devices, antibiotic use, or recent healthcare were not found.

Conclusion

We observed striking regional differences in occurrence of CTX-M-9 producing Enterobacteriaceae, suggesting that environmental influences and plasmid transfer may contribute to acquisition. It is worrisome that a large number of ESBL Enterobacteriaceae strains bearing CTX-M ESBLs circulate in the community among children.

Disclosures

All authors: No reported disclosures.

Emergence of Resistance to Colistin During the Treatment of Bloodstream Infection Caused by Klebsiella pneumoniae Carbapenemase-Producing Klebsiella pneumoniae

We report the emergence of colistin resistance in Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae after 8 days of colistin-based therapy, resulting in relapse of bloodstream infection and death. Disruption of the mgrB gene by insertion of a mobile genetic element was found to be the mechanism, which was replicated in vitro after exposure to subinhibitory concentrations of colistin and meropenem.

"Double carbapenem" and oral fosfomycin for the treatment of complicated urinary tract infections caused by blaNDM -harboring Enterobacteriaceae in kidney transplantation

Infections with carbapenemase-producing carbapenem-resistant Enterobacteriaceae represent an emergent problem worldwide. Treatment of infections caused by New Delhi metallo-beta-lactamase (NDM)-harboring Enterobacteriaceae is particularly challenging as it frequently involves the use of nephrotoxic agents, which is problematic in kidney transplant recipients and non-renal transplant patients with marginal kidney function. We present two cases of urinary tract infections caused by NDM-harboring Enterobacteriaceae successfully treated with a combination of "double carbapenem" and oral fosfomycin.

Evaluation of Sensititre Broth Microdilution Plate for determining the susceptibility of carbapenem-resistant Klebsiella pneumoniae to polymyxins

Colistin and polymyxin B MICs were determined for 106 carbapenem-resistant Klebsiella pneumoniae (CR-Kp) isolates using Sensititre Research Use Only GNX2F plates (Thermo Fisher) and compared to CLSI broth macrodilution (BMD) as the reference method. For colistin, EUCAST breakpoints were applied and testing of isolates with very major (VM) errors was repeated in duplicate by both methods to determine a majority result. Essential agreement (MIC ± one dilution) of GNX2F with the reference method was 97.1% for polymyxin B and 92.5% for colistin (7 VM errors, 22.6%). After discrepancy testing, there were 28 colistin resistant isolates by BMD and essential agreement was 94.3% with 4 VM errors (14.3%). Colistin and polymyxin B GNX2F results showed acceptable essential agreement with BMD for MICS without interpretation. Colistin VM errors with EUCAST breakpoints were due to MIC variability in the 2 to 4 μg/mL range that could be addressed by establishing an intermediate category.

A Prospective Observational Study of the Epidemiology, Management, and Outcomes of Skin and Soft Tissue Infections Due to Carbapenem-Resistant Enterobacteriaceae

Background

This study was performed to characterize the epidemiology, management, and outcomes of skin and soft tissue infection (SSTI) and colonization due to carbapenem-resistant Enterobacteriaceae (CRE).

Methods

Patients from the Consortium on Resistance Against Carbapenem in Klebsiella and Other Enterobacteriaceae (CRACKLE-1) from December 24, 2011 to October 1, 2014 with wound cultures positive for CRE were included in the study. Predictors of surgical intervention were analyzed. Molecular typing of isolates was performed using repetitive extragenic palindromic polymerase chain reaction (PCR). Carbapenemase genes were detected using PCR.

Results

One hundred forty-two patients were included: 62 had SSTI (44%) and 56% were colonized. Mean age was 61 years, and 48% were male: median Charlson score was 3 (interquartile range, 1–5). Forty-eight percent of patients were admitted from long-term care facilities (LTCFs), and 31% were from the community. Two strain types (ST258A and ST258B) were identified (73% of 45 tested). Carbapenemase genes were detected in 40 of 45 isolates (bla_KPC-3 [47%], bla_KPC-2 [42%]). Sixty-eight patients (48%) underwent surgical intervention, 63% of whom had SSTI. Patients admitted from LTCFs were less likely to undergo surgical intervention (odds ratio [OR], 0.36; 95% confidence interval [CI], 0.18–0.71). In multivariable analysis, among patients with SSTI, those admitted from LTCFs were less likely to undergo debridement (OR, 0.18; 95% CI, 0.04–0.93).

Conclusions

Patients admitted from LTCFs with CRE SSTI were less likely to undergo surgical intervention. Sixteen percent of the patients died, and approximately 50% of survivors required more intensive care upon discharge. These findings suggest a unique, impactful syndrome within the CRE infection spectrum. Further studies are needed to assess the role of surgical debridement in management of CRE-SSTI, particularly among LTCF residents.

Leading Antibacterial Laboratory Research by Integrating Conventional and Innovative Approaches: The Laboratory Center of the Antibacterial Resistance Leadership Group

The Antibacterial Resistance Leadership Group (ARLG) Laboratory Center (LC) leads the evaluation, development, and implementation of laboratory-based research by providing scientific leadership and supporting standard/specialized laboratory services. The LC has developed a physical biorepository and a virtual biorepository. The physical biorepository contains bacterial isolates from ARLG-funded studies located in a centralized laboratory and they are available to ARLG investigators. The Web-based virtual biorepository strain catalogue includes well-characterized gram-positive and gram-negative bacterial strains published by ARLG investigators. The LC, in collaboration with the ARLG Leadership and Operations Center, developed procedures for review and approval of strain requests, guidance during the selection process, and for shipping strains from the distributing laboratories to the requesting investigators. ARLG strains and scientific and/or technical guidance have been provided to basic research laboratories and diagnostic companies for research and development, facilitating collaboration between diagnostic companies and the ARLG Master Protocol for Evaluating Multiple Infection Diagnostics (MASTERMIND) initiative for evaluation of multiple diagnostic devices from a single patient sampling event. In addition, the LC has completed several laboratory-based studies designed to help evaluate new rapid molecular diagnostics by developing, testing, and applying a MASTERMIND approach using purified bacterial strains. In collaboration with the ARLG's Statistical and Data Management Center (SDMC), the LC has developed novel analytical strategies that integrate microbiologic and genetic data for improved and accurate identification of antimicrobial resistance. These novel approaches will aid in the design of future ARLG studies and help correlate pathogenic markers with clinical outcomes. The LC's accomplishments are the result of a successful collaboration with the ARLG's Leadership and Operations Center, Diagnostics and Devices Committee, and SDMC. This interactive approach has been pivotal for the success of LC projects.

Colistin Resistance in Carbapenem-Resistant Klebsiella pneumoniae: Laboratory Detection and Impact on Mortality

Background

Polymyxins including colistin are an important "last-line" treatment for infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKp). Increasing use of colistin has led to resistance to this cationic antimicrobial peptide.

Methods

A cohort nested within the Consortium on Resistance against Carbapenems in Klebsiella pneumoniae (CRACKLE) was constructed of patients with infection, or colonization with CRKp isolates tested for colistin susceptibility during the study period of December, 2011 to October, 2014. Reference colistin resistance determination as performed by broth macrodilution was compared to results from clinical microbiology laboratories (Etest) and to polymyxin resistance testing. Each patient was included once, at the time of their first colistin-tested CRKp positive culture. Time to 30-day in-hospital all-cause mortality was evaluated by Kaplan-Meier curves and Cox proportional hazard modeling.

Results

In 246 patients with CRKp, 13% possessed ColR CRKp. ColR was underestimated by Etest (very major error rate = 35%, major error rate = 0.4%). A variety of rep-PCR strain types were encountered in both the ColS and the ColR groups. Carbapenem resistance was mediated primarily by blaKPC-2 (46%) and blaKPC-3 (50%). ColR was associated with increased hazard for in-hospital mortality (aHR 3.48; 95% confidence interval, 1.73-6.57; P < .001). The plasmid-associated ColR genes, mcr-1 and mcr-2 were not detected in any of the ColR CRKp.

Conclusions

In this cohort, 13% of patients with CRKp presented with ColR CRKp. The apparent polyclonal nature of the isolates suggests de novo emergence of ColR in this cohort as the primary factor driving ColR. Importantly, mortality was increased in patients with ColR isolates.

Multidrug Resistant Pseudomonas aeruginosa Causing Prosthetic Valve Endocarditis: A Genetic-Based Chronicle of Evolving Antibiotic Resistance

A rare case of MDR P. aeruginosa causing PVE is analyzed at the genetic level with the goal of understanding acquired resistance mechanisms. The molecular basis of evolving antibiotic resistance gives clinicians insight into the nature of persistent P. aeruginosa infections.

Background. Successful treatment of infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa is thwarted by the emergence of antibiotic resistance and biofilm formation on prosthetic devices. Our aims were to decipher the molecular basis of resistance in a unique case of prosthetic valve endocarditis (PVE) caused by MDR P. aeruginosa.

Methods. Five sequential MDR P. aeruginosa blood isolates collected during a 7-month period were recovered from a patient suffering from PVE previously exposed to β-lactam antibiotics. Minimum inhibitory concentrations (MICs) of several classes of antibiotics were used to indicate clinical resistance characteristics; relatedness of the isolates was determined using multilocus sequence typing and repetitive sequence-based polymerase chain reaction. Amplification and sequencing of regulatory and resistance genes was performed.

Results. All isolates belonged to ST 298, possessed bla_PDC-16, and were resistant to fluoroquinolones and carbapenems. In the course of therapy, we observed a >2-fold increase in cephalosporin resistance (4 µg/mL to >16 µg/mL). Sequencing of the AmpC regulator, ampR, revealed a D135N point mutation in cephalosporin-resistant isolates. Common carbapenemase genes were not identified. All isolates demonstrated a premature stop codon at amino acid 79 of the outer membrane protein OprD and mutations in the quinolone resistance-determining regions of gyrA and parC. Point mutations in nalC, an efflux pump regulator, were also observed.

Conclusions. In this analysis, we chart the molecular evolution of β-lactam resistance in a case of PVE. We show that mutations in regulatory genes controlling efflux and cephalosporinase production contributed to the MDR phenotype.