Mechanisms of Resistance to Ceftolozane/Tazobactam in Pseudomonas aeruginosa: Results of the GERPA Multicenter Study

Treatment of infections caused by multidrug-resistant Gram-negative bacilli: A practical approach by the Italian (SIMIT) and French (SPILF) Societies of Infectious Diseases

INTRODUCTION

The emergence of multidrug-resistant Gram-negative bacilli and the development of new antibiotics have complicated the selection of optimal regimens. International guidelines are valuable tools, but are limited by the scarcity of high-quality randomized trials in many situations.

METHODS

A panel of experts from the French and Italian Societies of Infectious Diseases aimed to address unresolved issues in clinical practice based on their experience, an updated literature review and open discussions.

RESULTS

The panel reached consensus for the following 'first choices': (i) cefepime for ventilator-acquired pneumonia due to AmpC β-lactamase-producing Enterobacterales; (ii) the β-lactam/β-lactamase inhibitor combination most active in vitro, or cefiderocol combined with fosfomycin, and aerosolized colistin or aminoglycosides, for severe pneumonia due to Pseudomonas aeruginosa resistant to ceftolozane-tazobactam; (iii) high-dose piperacillin-tazobactam (including loading dose and continuous infusion) for complicated urinary tract infections (cUTIs) caused by extended-spectrum β-lactamase-producing Enterobacterales with piperacillin-tazobactam minimum inhibitory concentration (MIC) ≤8 mg/L; (iv) high-dose cefepime for cUTIs due to AmpC β-lactamase-producing Enterobacterales other than Enterobacter spp. if cefepime MIC ≤2 mg/L; (v) ceftolozane-tazobactam or ceftazidime-avibactam plus metronidazole for intra-abdominal infections (IAIs) due to third-generation cephalosporin-resistant Enterobacterales; (vi) ceftazidime-avibactam plus aztreonam plus metronidazole for IAIs due to metallo-β-lactamase-producing Enterobacterales; (vii) ampicillin-sulbactam plus colistin for bloodstream infections (BSIs) caused by carbapenem-resistant Acinetobacter baumannii; (viii) meropenem-vaborbactam for BSIs caused by Klebsiella pneumoniae carbapenemase-producing Enterobacterales; and (ix) ceftazidime-avibactam plus fosfomycin for neurological infections caused by carbapenem-resistant P. aeruginosa.

CONCLUSIONS

These expert choices were based on the necessary balance between antimicrobial stewardship principles and the need to provide optimal treatment for individual patients in each situation.

Proteomic assay for rapid characterisation of Staphylococcus aureus antimicrobial resistance mechanisms directly from blood cultures

PURPOSE

Staphylococcus aureus is one of the most common pathogens causing bloodstream infection. A rapid characterisation of resistance to methicillin and, occasionally, to aminoglycosides for particular indications, is therefore crucial to quickly adapt the treatment and improve the clinical outcomes of septic patients. Among analytical technologies, targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) has emerged as a promising tool to detect resistance mechanisms in clinical samples.

METHODS

A rapid proteomic method was developed to detect and quantify the most clinically relevant antimicrobial resistance effectors in S. aureus in the context of sepsis: PBP2a, PBP2c, APH(3')-III, ANT(4')-I, and AAC(6')-APH(2''), directly from positive blood cultures and in less than 70 min including a 30-min cefoxitin-induction step. The method was tested on spiked blood culture bottles inoculated with 124 S.aureus, accounting for the known genomic diversity of SCCmec types and the genetic background of the strains.

RESULTS

This method provided 99% agreement for PBP2a (n = 98/99 strains) detection. Agreement was 100% for PBP2c (n = 5/5), APH(3')-III (n = 16/16), and ANT(4')-I (n = 20/20), and 94% for AAC(6')-APH(2'') (n = 16/17). Across the entire strain collection, 100% negative agreement was reported for each of the 5 resistance proteins. Additionally, relative quantification of ANT(4')-I expression allowed to discriminate kanamycin-susceptible and -resistant strains, in all strains harbouring the ant(4')-Ia gene.

CONCLUSION

The LC-MS/MS method presented herein demonstrates its ability to provide a reliable determination of S. aureus resistance mechanisms, directly from positive blood cultures and in a short turnaround time, as required in clinical laboratories.

In vitro development of resistance against antipseudomonal agents: comparison of novel β-lactam/β-lactamase inhibitor combinations and other β-lactam agents

We subjected seven P. aeruginosa isolates to a 10-day serial passaging against five antipseudomonal agents to evaluate resistance levels post-exposure and putative resistance mechanisms in terminal mutants were analyzed by whole-genome sequencing analysis. Meropenem (mean, 38-fold increase), cefepime (14.4-fold), and piperacillin-tazobactam (52.9-fold) terminal mutants displayed high minimum inhibitory concentration (MIC) values compared to those obtained after exposure to ceftolozane-tazobactam (11.4-fold) and ceftazidime-avibactam (5.7-fold). Fewer isolates developed elevated MIC values for other β-lactams and agents belonging to other classes when exposed to meropenem in comparison to other agents. Alterations in nalC and nalD, involved in the upregulation of the efflux pump system MexAB-OprM, were common and observed more frequently in isolates exposed to ceftazidime-avibactam and meropenem. These alterations, along with ones in mexR and amrR, provided resistance to most β-lactams and levofloxacin but not imipenem. The second most common gene altered was mpl, which is involved in the recycling of the cell wall peptidoglycan. These alterations were mainly noted in isolates exposed to ceftolozane-tazobactam and piperacillin-tazobactam but also in one cefepime-exposed isolate. Alterations in other genes known to be involved in β-lactam resistance (ftsI, oprD, phoP, pepA, and cplA) and multiple genes involved in lipopolysaccharide biosynthesis were also present. The data generated here suggest that there is a difference in the mechanisms selected for high-level resistance between newer β-lactam/β-lactamase inhibitor combinations and older agents. Nevertheless, the isolates exposed to all agents displayed elevated MIC values for other β-lactams (except imipenem) and quinolones tested mainly due to alterations in the MexAB-OprM regulators that extrude these agents.

Assessing the impact of meropenem exposure on ceftolozane/tazobactam-resistance development in Pseudomonas aeruginosa using in vitro serial passage

BACKGROUND

Patients infected with difficult-to-treat Pseudomonas aeruginosa are likely to receive meropenem (MEM) empirically before escalation to ceftolozane/tazobactam (C/T). We assessed whether pre-exposure to MEM affected C/T resistance development on C/T exposure.

MATERIALS AND METHODS

Nine clinical P. aeruginosa isolates were exposed to MEM 16 mg/L for 72 h. Then, isolates were serially passaged in the presence of C/T (concentration of 10 mg/L) for 72 h as two groups: an MEM-exposed group inoculated with MEM pre-exposed isolates and a non-MEM control group. At 24 h intervals, samples were plated on drug-free and drug-containing agar (C/T concentration 16/8 mg/L) and incubated to quantify bacterial densities (log10 cfu/mL). Growth on C/T agar indicated resistance development, and resistant population was calculated by dividing the cfu/mL on C/T plates by the cfu/mL on drug-free agar.

RESULTS

At 72 h, resistant populations were detected in 6/9 isolates. In five isolates, MEM exposure significantly increased the prevalence of ceftolozane/tazobactam-resistance development; the percentages of resistance population were 100%, 100%, 53.5%, 31% and 3% for the MEM-exposed versus 0%, 0%, 2%, 0.35% and ≤0.0003% in the unexposed groups. One isolate had a similar resistant population at 72 h between the two groups. The remaining isolates showed no development of resistance, regardless of previous MEM exposure.

CONCLUSIONS

MEM exposure may pre-dispose to C/T resistance development and thus limit the therapeutic utility of this β-lactam/β-lactamase inhibitor. Resistance may be a result of stress exposure or molecular-level mutations conferring cross-resistance. Further in vivo studies are needed to assess clinical implications of these findings.

Antimicrobial and Diagnostic Stewardship of the Novel β-Lactam/β-Lactamase Inhibitors for Infections Due to Carbapenem-Resistant Enterobacterales Species and Pseudomonas aeruginosa

Carbapenem-resistant Gram-negative bacterial infections are a major public health threat due to the limited therapeutic options available. The introduction of the new β-lactam/β-lactamase inhibitors (BL/BLIs) has, however, altered the treatment options for such pathogens. Thus, four new BL/BLI combinations-namely, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/relebactam, and ceftolozane/tazobactam-have been approved for infections attributed to carbapenem-resistant Enterobacterales species and Pseudomonas aeruginosa. Nevertheless, although these antimicrobials are increasingly being used in place of other drugs such as polymyxins, their optimal clinical use is still challenging. Furthermore, there is evidence that resistance to these agents might be increasing, so urgent measures should be taken to ensure their continued effectiveness. Therefore, clinical laboratories play an important role in the judicious use of these new antimicrobial combinations by detecting and characterizing carbapenem resistance, resolving the presence and type of carbapenemase production, and accurately determining the minimum inhibitor concentrations (MICs) for BL/BLIs. These three targets must be met to ensure optimal BL/BLIs use and prevent unnecessary exposure that could lead to the development of resistance. At the same time, laboratories must ensure that results are interpreted in a timely manner to avoid delays in appropriate treatment that might be detrimental to patient safety. Thus, we herein present an overview of the indications and current applications of the new antimicrobial combinations and explore the diagnostic limitations regarding both carbapenem resistance detection and the interpretation of MIC results. Moreover, we suggest the use of alternative narrower-spectrum antibiotics based on susceptibility testing and present data regarding the effect of synergies between BL/BLIs and other antimicrobials. Finally, in order to address the absence of a standardized approach to using the novel BL/BLIs, we propose a diagnostic and therapeutic algorithm, which can be modified based on local epidemiological criteria. This framework could also be expanded to incorporate other new antimicrobials, such as cefiderocol, or currently unavailable BL/BLIs such as aztreonam/avibactam and cefepime/taniborbactam.

Outbreak of Pseudomonas aeruginosa High-Risk Clone ST309 Serotype O11 Featuring blaPER-1 and qnrVC6

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections worldwide. Biofilm production, antibiotic resistance, and a wide range of virulence factors contribute to their persistence in nosocomial environments. We describe an outbreak caused by a multidrug-resistant P. aeruginosa strain in an ICU. Antibiotic susceptibility was determined and blaPER-1 and qnrVC were amplified via PCR. Clonality was determined using PFGE and biofilm formation was studied with a static model. A combination of antibiotics was assessed on both planktonic cells and biofilms. WGS was performed on five isolates. All isolates were clonally related, resistant to ceftazidime, cefepime, amikacin, and ceftolozane-tazobactam, and harbored blaPER-1; 11/19 possessed qnrVC. Meropenem and ciprofloxacin reduced the biofilm biomass; however, the response to antibiotic combinations with rifampicin was different between planktonic cells and biofilms. WGS revealed that the isolates belonged to ST309 and serotype O11. blaPER-1 and qnrVC6 were associated with a tandem of ISCR1 as part of a complex class one integron, with aac(6')-Il and ltrA as gene cassettes. The structure was associated upstream and downstream with Tn4662 and flanked by direct repeats, suggesting its horizontal mobilization capability as a composite transposon. ST309 is considered an emerging high-risk clone that should be monitored in the Americas.

Whole genome sequencing of resistance and virulence genes in multi-drug resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is an opportunistic bacterium that causes serious hospital-acquired infections. To assess the risk of clinically isolated P. aeruginosa to human health, we analyzed the resistance and virulence mechanisms of a collection of clinical isolates.

METHODS

This was a retrospective study in which P. aeruginosa isolates collected from January 1, 2018 to August 31, 2019 were analyzed using phenotypic and whole-genome sequencing (WGS) methods. The analysis included 48 clinical samples. Median patient age was 54.0 (29.5) years, and 58.3% of patients were women. Data from the microbiology laboratory database were reviewed to identify P. aeruginosa isolates. All unique isolates available for further testing were included, and related clinical data were collected. Infections were defined as hospital acquired if the index culture was obtained at least 48 h after hospitalization.

RESULTS

High-risk P. aeruginosa clones, including sequence types (STs) ST235 and ST111, were identified, in addition to 12 new STs. The isolates showed varying degrees of biofilm formation ability when evaluated at room temperature, along with reduced metabolic activity, as measured by metabolic staining, suggesting their ability to evade antimicrobial therapy. Most isolates (77.1%) were multidrug resistant (MDR), with the highest resistance and susceptibility rates to beta-lactams and colistimethate sodium, respectively.

CONCLUSIONS

The MDR phenotypes of the examined isolates can be explained by the high prevalence of efflux-mediated resistance- and hydrolytic enzyme-encoding genes. These isolates had high cytotoxic potential, as indicated by the detection of toxin production-related genes.

Approaches to Testing Novel β-Lactam and β-Lactam Combination Agents in the Clinical Laboratory

The rapid emergence of multi-drug resistant Gram-negative pathogens has driven the introduction of novel β-lactam combination agents (BLCs) to the antibiotic market: ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, and sulbactam-durlobactam. These agents are equipped with innovative mechanisms that confer broad Gram-negative activity, notably against certain challenging carbapenemases. While their introduction offers a beacon of hope, clinical microbiology laboratories must navigate the complexities of susceptibility testing for these agents due to their diverse activity profiles against specific β-lactamases and the possibility of acquired resistance mechanisms in some bacterial isolates. This review explores the complexities of these novel antimicrobial agents detailing the intricacies of their application, providing guidance on the nuances of susceptibility testing, interpretation, and result reporting in clinical microbiology laboratories.

Natural protein engineering in the Ω-loop: the role of Y221 in ceftazidime and ceftolozane resistance in Pseudomonas-derived cephalosporinase

A wide variety of clinically observed single amino acid substitutions in the Ω-loop region have been associated with increased minimum inhibitory concentrations and resistance to ceftazidime (CAZ) and ceftolozane (TOL) in Pseudomonas-derived cephalosporinase and other class C β-lactamases. Herein, we demonstrate the naturally occurring tyrosine to histidine substitution of amino acid 221 (Y221H) in Pseudomonas-derived cephalosporinase (PDC) enables CAZ and TOL hydrolysis, leading to similar kinetic profiles (k cat = 2.3 ± 0.2 µM and 2.6 ± 0.1 µM, respectively). Mass spectrometry of PDC-3 establishes the formation of stable adducts consistent with the formation of an acyl enzyme complex, while spectra of E219K (a well-characterized, CAZ- and TOL-resistant comparator) and Y221H are consistent with more rapid turnover. Thermal denaturation experiments reveal decreased stability of the variants. Importantly, PDC-3, E219K, and Y221H are all inhibited by avibactam and the boronic acid transition state inhibitors (BATSIs) LP06 and S02030 with nanomolar IC50 values and the BATSIs stabilize all three enzymes. Crystal structures of PDC-3 and Y221H as apo enzymes and complexed with LP06 and S02030 (1.35-2.10 Å resolution) demonstrate ligand-induced conformational changes, including a significant shift in the position of the sidechain of residue 221 in Y221H (as predicted by enhanced sampling well-tempered metadynamics simulations) and extensive hydrogen bonding between the enzymes and BATSIs. The shift of residue 221 leads to the expansion of the active site pocket, and molecular docking suggests substrates orientate differently and make different intermolecular interactions in the enlarged active site compared to the wild-type enzyme.

Combined genomic-proteomic approach in the identification of Campylobacter coli amoxicillin-clavulanic acid resistance mechanism in clinical isolates

Introduction

Aminopenicillins resistance among Campylobacter jejuni and Campylobacter coli strains is associated with a single mutation in the promoting region of a chromosomal beta-lactamase blaOXA61, allowing its expression. Clavulanic acid is used to restore aminopenicillins activity in case of blaOXA61 expression and has also an inherent antimicrobial activity over Campylobacter spp. Resistance to amoxicillin-clavulanic acid is therefore extremely rare among these species: only 0.1% of all Campylobacter spp. analyzed in the French National Reference Center these last years (2017-2022).

Material and methods

Whole genome sequencing with bioinformatic resistance identification combined with mass spectrometry (MS) was used to identify amoxicillin-acid clavulanic resistance mechanism in Campylobacters.

Results

A G57T mutation in blaOXA61 promoting region was identified in all C. jejuni and C. coli ampicillin resistant isolates and no mutation in ampicillin susceptible isolates. Interestingly, three C. coli resistant to both ampicillin and amoxicillin-clavulanic acid displayed a supplemental deletion in the promoting region of blaOXA61 beta-lactamase, at position A69. Using MS, a significant difference in the expression of BlaOXA61 was observed between these three isolates and amoxicillin-clavulanic acid susceptible C. coli.

Conclusion

A combined genomics/proteomics approach allowed here to identify a rare putative resistance mechanism associated with amoxicillin-clavulanic acid resistance for C. coli.

Biomolecular interactions between the antibacterial ceftolozane and the human inflammatory disease target ADAM17: a drug repurposing study

Inhibition of a disintegrin and metalloproteinase-17 (ADAM17), a metzincin, is proposed as a novel therapeutic strategy to suppress overproduction of the proinflammatory cytokine TNF-α in rheumatoid arthritis and inflammatory bowel disease. Existing ADAM17 inhibitors generate toxic metabolites in-vivo or haven't progressed in clinical trials. Previous studies suggest that ligands which bind to ADAM17 active site by interacting with the Zn ion and L-shaped hydrophobic S1'- and S3'-pockets and forming favorable hydrogen bonds could act as potential ADAM17 inhibitors. Here, we investigated whether the FDA-approved anti-bacterial drug ceftolozane, a cephalosporin containing aromatic groups and carboxyl groups as probable zinc binding groups (ZBGs), forms non-covalent interactions resulting in its binding in the active site of ADAM17. In this study, the density functional theory (DFT), molecular docking and molecular dynamics calculations with the catalytic chain of ADAM17 show that carboxyl group of ceftolozane acts as moderate ZBG, and its extended geometry forms hydrogen bonds and hydrophobic interactions resulting in a binding affinity comparable to the co-crystallized known ADAM17 inhibitor. The favorable binding interactions identified here suggest the potential of ceftolozane to modulate ADAM17 activity in inflammatory diseases. ADAM17 cleaves and releases epidermal growth factor (EGF) ligands from the cell surface. The shed EGF ligands then bind to the EGF receptors to drive embryonic development. Therefore, our findings also suggest that use of ceftolozane during pregnancy may inhibit ADAM17-mediated shedding of EGF and thus increase the risk of birth defects in humans.Communicated by Ramaswamy H. Sarma.

Cefiderocol activity is compromised by acquired extended-spectrum oxacillinases in Pseudomonas aeruginosa

OBJECTIVES

Cefiderocol has an excellent in vitro activity on clinical strains of Pseudomonas aeruginosa (P. aeruginosa). However, the resistance of some isolates has been associated with the production of some β-lactamases. Whether some acquired extended-spectrum oxacillinases (ES-OXA) common in this species may compromise the susceptibility of P. aeruginosa to cefiderocol has not been evaluated so far.

METHODS

Eighteen genes encoding OXA belonging to the major subgroups identified in P. aeruginosa OXA-1 (n = 3); - 2 (n = 5); - 10 (n = 8), and - 46 (n = 2) were cloned into pUCP24 shuttle vector and transferred into reference strain PAO1.

RESULTS

Although production of the OXA-1 subgroup enzymes did not alter cefiderocol MICs, the β-lactamases of OXA-2, OXA-46, and four variants of the OXA-10 subgroup resulted in an 8-fold to 32-fold decrease in susceptibility in the PAO1 background. Interestingly, point mutations Ala149Pro and Asp150Gly in OXA-2 subgroup, Trp154Cys and Gly157Asp in OXA-10 subgroup (all located in the Ω loop), and the duplication of a Thr206 and a Gly207 in the β5-β6 loop of OXA-10 subgroup were related to decreased susceptibility to cefiderocol. We also showed that some ES-OXA, including the most frequent ES-OXA in P. aeruginosa strains, OXA-19 (derived from OXA-10 subgroup), significantly compromised activity of cefiderocol in addition to ceftazidime, ceftolozane/tazobactam, and ceftazidime/avibactam in clinical strains.

CONCLUSION

This work shows that several ES-OXA have a significant effect on cefiderocol susceptibility. Of concern are the Trp154Cys and Gly157Asp mutations that occur in some of these β-lactamases, as they are associated with a decreased activity of the most recent cephalosporins introduced to combat P. aeruginosa infections.

Temporal and geographical prevalence of carbapenem-resistant Pseudomonas aeruginosa and the in vitro activity of ceftolozane/tazobactam and comparators in Taiwan-SMART 2012-2021

OBJECTIVES

To determine the in vitro activities of ceftolozane/tazobactam (C/T) and comparators against Pseudomonas aeruginosa isolates cultured from hospitalised patient samples in Taiwan from 2012 to 2021 with an additional focus on the temporal and geographical prevalence of carbapenem-resistant P. aeruginosa (CRPA).

METHODS

P. aeruginosa isolates (n = 3013) were collected annually by clinical laboratories in northern (two medical centres), central (three medical centres), and southern Taiwan (four medical centres) as part of the SMART global surveillance program. MICs were determined by CLSI broth microdilution and interpreted using 2022 CLSI breakpoints. Molecular β-lactamase gene identification was performed on selected non-susceptible isolate subsets in 2015 and later.

RESULTS

Overall, 520 (17.3%) CRPA isolates were identified. The prevalence of CRPA increased from 11.5%-12.3% (2012-2015) to 19.4%-22.8% (2018-2021) (P ≤ 0.0001). Medical centres in northern Taiwan reported the highest percentages of CRPA. C/T, first tested in the SMART program in 2016, was highly active against all P. aeruginosa (97% susceptible), with annual susceptibility rates ranging from 94% (2017) to 99% (2020). Against CRPA, C/T inhibited >90% of isolates each year, with the exception of 2017 (79.4% susceptible). Most CRPA isolates (83%) were molecularly characterised, and only 2.1% (9/433) carried a carbapenemase (most commonly, VIM); all nine carbapenemase-positive isolates were from northern and central Taiwan.

CONCLUSION

The prevalence of CRPA increased significantly in Taiwan from 2012 to 2021 and warrants continued monitoring. In 2021, 97% of all P. aeruginosa and 92% of CRPA in Taiwan were C/T susceptible. Routine in vitro susceptibility testing of clinical isolates of P. aeruginosa against C/T, and other newer β-lactam/β-lactamase inhibitor combinations, appears prudent.

Rationale and evidence for the use of new beta-lactam/beta-lactamase inhibitor combinations and cefiderocol in critically ill patients

BACKGROUND

Healthcare-associated infections involving Gram-negative bacteria (GNB) with difficult-to-treat resistance (DTR) phenotype are associated with impaired patient-centered outcomes and poses daily therapeutic challenges in most of intensive care units worldwide. Over the recent years, four innovative β-lactam/β-lactamase inhibitor (BL/BLI) combinations (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of certain DTR-GNB infections. The literature addressing their microbiological spectrum, pharmacokinetics, clinical efficacy and safety was exhaustively audited by our group to support the recent guidelines of the French Intensive Care Society on their utilization in critically ill patients. This narrative review summarizes the available evidence and unanswered questions on these issues.

METHODS

A systematic search for English-language publications in PUBMED and the Cochrane Library database from inception to November 15, 2022.

RESULTS

These drugs have demonstrated relevant clinical success rates and a reduced renal risk in most of severe infections for whom polymyxin- and/or aminoglycoside-based regimen were historically used as last-resort strategies-namely, ceftazidime-avibactam for infections due to Klebsiella pneumoniae carbapenemase (KPC)- or OXA-48-like-producing Enterobacterales, meropenem-vaborbactam for KPC-producing Enterobacterales, ceftazidime-avibactam/aztreonam combination or cefiderocol for metallo-β-lactamase (MBL)-producing Enterobacterales, and ceftolozane-tazobactam, ceftazidime-avibactam and imipenem-relebactam for non-MBL-producing DTR Pseudomonas aeruginosa. However, limited clinical evidence exists in critically ill patients. Extended-infusion scheme (except for imipenem-relebactam) may be indicated for DTR-GNB with high minimal inhibitory concentrations and/or in case of augmented renal clearance. The potential benefit of combining these agents with other antimicrobials remains under-investigated, notably for the most severe presentations. Other important knowledge gaps include pharmacokinetic information in particular situations (e.g., pneumonia, other deep-seated infections, and renal replacement therapy), the hazard of treatment-emergent resistance and possible preventive measures, the safety of high-dose regimen, the potential usefulness of rapid molecular diagnostic tools to rationalize their empirical utilization, and optimal treatment durations. Comparative clinical, ecological, and medico-economic data are needed for infections in whom two or more of these agents exhibit in vitro activity against the causative pathogen.

CONCLUSIONS

New BL/BLI combinations and cefiderocol represent long-awaited options for improving the management of DTR-GNB infections. Several research axes must be explored to better define the positioning and appropriate administration scheme of these drugs in critically ill patients.

In Vivo Development of Aztreonam Resistance in Meropenem-Resistant Pseudomonas aeruginosa Owing to Overexpression of the blaPDC-16

The rapid acquisition of antibiotic resistance of Pseudomonas aeruginosa has been a complex problem in clinics. Two meropenem-resistant P. aeruginosa isolates were collected from the same patient on May 24, 2021, and June 4, 2021, respectively. The first was susceptible to aztreonam, while the second displayed resistance. This study aimed to identify the genetic differences between two P. aeruginosa isolates and uncover alterations formed by the within-host bacterial evolution leading to aztreonam resistance during therapy. Strains were subjected to antimicrobial susceptibility testing using the broth microdilution method. Genomic DNAs were obtained to identify their genetic differences. The relative mRNA levels of β-lactam-resistance genes were determined by real-time PCR. Both isolates belonged to ST 773 high-risk clones with the same antibiotic resistance genes, eliminating the possibility of horizontally obtaining resistance genes. Reverse transcription (RT)-PCR results showed that the blaPDC-16 mRNA level in the second one was about 1,500 times higher than that in the first one. When 3-aminophenyl boronic acid was added, the second strain recovered its susceptibility to aztreonam, which confirmed that the overexpression of blaPDC-16 was the main reason for the isolate's resistance to aztreonam. Compared to the first strain, the second showed a single amino acid substitution in AmpR located upstream of blaPDC-16, which may contribute to the upregulation of blaPDC-16 and lead to aztreonam resistance. AmpR plays an essential role in regulating antibiotic resistance in P. aeruginosa, and there is a need to be alert to clinical treatment failures associated with mutations in ampR. IMPORTANCE Pseudomonas aeruginosa is notorious for being highly resistant to antimicrobial agents. In this study, two P. aeruginosa strains isolated from the same patient with different susceptibility to aztreonam were used to illustrate the within-host resistance evolution process of P. aeruginosa. Both isolates, which belonged to a ST773 high-risk clone, had the same β-lactam resistance genes (blaPDC-16, blaIMP-45, blaOXA-1, and blaOXA-395), which means the second isolate might have been derived from the first isolate by gaining aztreonam resistance via mutations associated with aztreonam resistance relative genes. Subsequently, we found that mutation in ampR may be the cause of aztreonam resistance in the second isolate. Mutation in ampR leads to its loss of control over blaPDC-16, allowing overexpression of blaPDC-16 and further resistance to aztreonam. This study revealed that ampR plays an essential role in regulating antibiotic resistance in P. aeruginosa. There is a need to be alert to clinical treatment failures associated with mutations in ampR.

Susceptibility profile and β-lactamase content of global Pseudomonas aeruginosa isolates resistant to ceftolozane/tazobactam and/or imipenem/relebactam-SMART 2016-21

Objectives

To determine susceptibility profiles and β-lactamase content for ceftolozane/tazobactam-resistant and imipenem/relebactam-resistant Pseudomonas aeruginosa isolates collected in eight global regions during 2016-21.

Methods

Broth microdilution MICs were interpreted using CLSI breakpoints. PCR to identify β-lactamase genes or WGS was performed on selected isolate subsets.

Results

Ceftolozane/tazobactam-resistant [from 0.6% (Australia/New Zealand) to 16.7% (Eastern Europe)] and imipenem/relebactam-resistant [from 1.3% (Australia/New Zealand) to 13.6% (Latin America)] P. aeruginosa varied by geographical region. Globally, 5.9% of isolates were both ceftolozane/tazobactam resistant and imipenem/relebactam resistant; 76% of these isolates carried MBLs. Most ceftolozane/tazobactam-resistant/imipenem/relebactam-susceptible isolates carried ESBLs (44%) or did not carry non-intrinsic (acquired) β-lactamases (49%); 95% of imipenem/relebactam-resistant/ceftolozane/tazobactam-susceptible isolates did not carry non-intrinsic β-lactamases. Isolates that carried indicators of strong PDC (Pseudomonas-derived cephalosporinase) up-regulation without a mutation known to expand the spectrum of PDC, or non-intrinsic β-lactamases, showed an 8-fold increase in ceftolozane/tazobactam modal MIC; however, this rarely (3%) resulted in ceftolozane/tazobactam resistance. Isolates with a PDC mutation and an indicator for PDC upregulation were ceftolozane/tazobactam non-susceptible (MIC,  ≥ 8 mg/L). MICs ranged widely (1 to >32 mg/L) for isolates with a PDC mutation and no positively identified indicator for PDC up-regulation. Imipenem/relebactam-resistant/ceftolozane/tazobactam-susceptible isolates without non-intrinsic β-lactamases frequently (91%) harboured genetic lesions implying OprD loss of function; however, this finding alone did not account for this phenotype. Among imipenem-non-susceptible isolates without non-intrinsic β-lactamases, implied OprD loss only shifted the distribution of imipenem/relebactam MICs up by 1-2 doubling dilutions, resulting in ∼10% imipenem/relebactam-resistant isolates.

Conclusions

P. aeruginosa with ceftolozane/tazobactam-resistant/imipenem/relebactam-susceptible and imipenem/relebactam-resistant/ceftolozane/tazobactam-susceptible phenotypes were uncommon and harboured diverse resistance determinants.

Pharmacokinetics/pharmacodynamics and therapeutic drug monitoring of ceftazidime/avibactam administered by continuous infusion in patients with MDR Gram-negative bacterial infections

BACKGROUND

Therapeutic drug monitoring (TDM) of β-lactams in critically ill patients has been correlated with better clinical outcomes. Evidence on TDM of newer β-lactams such as ceftazidime/avibactam administered by continuous infusion (CI) is very limited.

OBJECTIVES

To describe our experience with TDM of ceftazidime/avibactam and pharmacokinetic/pharmacodynamic (PK/PD) target attainment in patients with MDR bacterial infections. Clinical outcomes of ceftazidime/avibactam administered by CI were also assessed.

METHODS

Patients treated with ceftazidime/avibactam administered by CI and undergoing TDM of ceftazidime plasma concentrations were included. Blood samples were obtained as part of the TDM program. The PK/PD therapeutic target of ceftazidime/avibactam was defined as 100%fT > 4 × MIC of the causative pathogen, and 100%fT > 10 × MIC was considered overexposure. Dose changes were made according to the TDM results.

RESULTS

Thirty-one patients were included. Ceftazidime/avibactam total daily doses ranged from 1 g/0.25 g to 6 g/1.5 g. Twenty-six patients (83.9%) achieved a 100%fT > 4 × MIC, 15 (48.4%) of which were overexposed (100%fT > 10 × MIC). Dose reduction was suggested in 16/28 (57.1%) patients and dose maintenance in 12/28 (42.9%). Overall clinical cure was observed in 21 (67.7%) patients, and 18 of these (85.7%) achieved a 100%fT > 4 × MIC.

CONCLUSIONS

Administering ceftazidime/avibactam by CI enabled the desired PK/PD target to be achieved in a large proportion of patients, even at lower doses than those recommended for a 2 h extended infusion. We suggest that the use of CI with TDM may be a useful tool for reducing initial doses, which could help to reduce antimicrobial-related adverse effects and treatment costs.

Molecular mechanisms leading to ceftolozane/tazobactam resistance in clinical isolates of Pseudomonas aeruginosa from five Latin American countries

Objectives

Identify molecular mechanisms responsible for the in vitro non-susceptibility to ceftolozane/tazobactam (TOL) in a group of 158 clinical isolates of Pseudomonas aeruginosa from five Latin American countries collected before the introduction of TOL into the clinical practice.

Methods

Clinical isolates of P. aeruginosa (n = 504) were collected between January 2016 and October 2017 from 20 hospitals located in Argentina, Brazil, Chile, Colombia, and Mexico. Minimum inhibitory concentrations (MICs) to TOL were determined by standard broth microdilution and interpreted according to CLSI breakpoints. Initially, production of carbapenemases in TOL non-susceptible isolates was assessed by Rapidec® followed by qPCR to detect bla_KPC, bla_NDM-1, bla_VIM, and bla_IMP. Illumina® WGS was performed for isolates in which non-susceptibility to TOL was not mediated by carbapenemases.

Results

A total of 158 (31.3%) isolates were non-susceptible to TOL. In 74 (46.8%) of these isolates, non-susceptibility to TOL was explained by the production of at least one carbapenemase. WGS revealed that some isolates carried ESBLs, mutated bla_PDC and ampD, associated with decreased susceptibility to TOL.

Conclusion

Substitutions found in PDC and carbapenemase production were the most common presumed mechanisms of resistance to TOL detected in this study. This study shows that epidemiological surveillance is warranted to monitor the emergence of novel mechanisms of resistance to TOL that might compromise its clinical utility.

Clinical Characteristics and Outcome of MDR/XDR Bacterial Infections in a Neuromuscular Semi-Intensive/Sub-Intensive Care Unit

(1) Background: The aim of this study was to assess the clinical and microbiological characteristics of multidrug-resistant infections in a neuromuscular semi-intensive/sub-intensive care unit; (2) Methods: Retrospective analysis on data from 18 patients with NMD with proven MDRO/XDRO colonisation/infection from August 2021 to March 2022 was carried out; (3) Results: Ten patients were males (55.6%), with a median age of 54 years, and there were fourteen patients (77.8%) with amyotrophic lateral sclerosis. All patients had at least one invasive device. Ten (55.6%) patients developed MDRO/XDRO infection (with a median time of 24 days) while six (33.3%) were colonised. The Charlson comorbidity index was >2 in both groups but higher in the infected compared with the colonised (4.5 vs. 3). Infected patients were mostly females (seven patients) with a median age of 62 years. The most common pathogens were Acinetobacter baumannii and Pseudomonas aeruginosa, infecting four (28.6%) patients each. Of eighteen infectious episodes, nine were pneumonia (hospital-acquired in seven cases). Colistin was the most commonly active antibiotic while carbapenems were largely inactive. Eradication of infection occurred in seven infectious episodes (38.9%). None of those with infection died; (4) Conclusions: MDRO/XDRO infections are common in patients with neuromuscular diseases, with carbapenem-resistant non-fermenting Gram-negative bacilli prevailing. These infections were numerically associated with the female sex, greater age, and comorbidities. Both eradication and infection-related mortality appeared low. We highlight the importance of infection prevention in this vulnerable population.

Role of the multi-drug efflux systems on the baseline susceptibility to ceftazidime/avibactam and ceftolozane/tazobactam in clinical isolates of non-carbapenemase-producing carbapenem-resistant Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is one of the pathogens that urgently needs new drugs and new alternatives for its control. The primary strategy to combat this bacterium is combining treatments of beta-lactam with a beta-lactamase inhibitor. The most used combinations against P. aeruginosa are ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T). Although mechanisms leading to CZA and C/T resistance have already been described, among which are the resistance-nodulation-division (RND) efflux pumps, the role that these extrusion systems may play in CZA, and C/T baseline susceptibility of clinical isolates remains unknown. For this purpose, 161 isolates of non-carbapenemase-producing (Non-CP) CRPA were selected, and susceptibility tests to CZA and C/T were performed in the presence and absence of the RND efflux pumps inhibitor, Phenylalanine-arginine β-naphthylamide (PAβN). In the absence of PAβN, C/T showed markedly higher activity against Non-CP-CRPA isolates than observed for CZA. These results were even more evident in isolates classified as extremely-drug resistant (XDR) or with difficult-to-treat resistance (DTR), where CZA decreased its activity up to 55.2% and 20.0%, respectively, whereas C/T did it up to 82.8% (XDR), and 73.3% (DTR). The presence of PAβN showed an increase in both CZA (37.6%) and C/T (44.6%) activity, and 25.5% of Non-CP-CRPA isolates increased their susceptibility to these two combined antibiotics. However, statistical analysis showed that only the C/T susceptibility of Non-CP-CRPA isolates was significantly increased. Although the contribution of RND activity to CZA and C/T baseline susceptibility was generally low (two-fold decrease of minimal inhibitory concentrations [MIC]), a more evident contribution was observed in a non-minor proportion of the Non-CP-CRPA isolates affected by PAβN [CZA: 25.4% (15/59); C/T: 30% (21/70)]. These isolates presented significantly higher MIC values for C/T. Therefore, we conclude that RND efflux pumps are participating in the phenomenon of baseline susceptibility to CZA and, even more, to C/T. However, the genomic diversity of clinical isolates is so great that deeper analyzes are necessary to determine which elements are directly involved in this phenomenon.

In vitro activity of imipenem/relebactam against Pseudomonas aeruginosa isolates recovered from ICU patients in Spain and Portugal (SUPERIOR and STEP studies)

OBJECTIVES

To study the in vitro activity of imipenem/relebactam and comparators and the imipenem/relebactam resistance mechanisms in a Pseudomonas aeruginosa collection from Portugal (STEP, 2017-18) and Spain (SUPERIOR, 2016-17) surveillance studies.

METHODS

P. aeruginosa isolates (n = 474) were prospectively recovered from complicated urinary tract (cUTI), complicated intra-abdominal (cIAI) and lower respiratory tract (LRTI) infections in 11 Portuguese and 8 Spanish ICUs. MICs were determined (ISO broth microdilution). All imipenem/relebactam-resistant P. aeruginosa isolates (n = 30) and a subset of imipenem/relebactam-susceptible strains (n = 32) were characterized by WGS.

RESULTS

Imipenem/relebactam (93.7% susceptible), ceftazidime/avibactam (93.5% susceptible) and ceftolozane/tazobactam (93.2% susceptible) displayed comparable activity. The imipenem/relebactam resistance rate was 6.3% (Portugal 5.8%; Spain 8.9%). Relebactam restored imipenem susceptibility to 76.9% (103/134) of imipenem-resistant isolates, including MDR (82.1%; 32/39), XDR (68.8%; 53/77) and difficult-to-treat (DTR) isolates (67.2%; 45/67). Among sequenced strains, differences in population structure were detected depending on the country: clonal complex (CC)175 and CC309 in Spain and CC235, CC244, CC348 and CC253 in Portugal. Different carbapenemase gene distributions were also found: VIM-20 (n = 3), VIM-1 (n = 2), VIM-2 (n = 1) and VIM-36 (n = 1) in Spain and GES-13 (n = 13), VIM-2 (n = 3) and KPC-3 (n = 2) in Portugal. GES-13-CC235 (n = 13) and VIM type-CC175 (n = 5) associations were predominant in Portugal and Spain, respectively. Imipenem/relebactam showed activity against KPC-3 strains (2/2), but was inactive against all GES-13 producers and most of the VIM producers (8/10). Mutations in genes affecting porin inactivation, efflux pump overexpression and LPS modification might also be involved in imipenem/relebactam resistance.

CONCLUSIONS

Microbiological results reinforce imipenem/relebactam as a potential option to treat cUTI, cIAI and LRTI caused by MDR/XDR P. aeruginosa isolates, except for GES-13 and VIM producers.

Treatment of severe multi-drug resistant Pseudomonas aeruginosa infections

Pseudomonas aeruginosa is the microorganism most frequently involved in the main ICU-acquired infections, with special importance in ventilator associated pneumonia. Its importance lies, in addition to its high incidence in critically ill patients, in the severity of the infections it causes and in the difficulty of its antimicrobial treatment, directly related to the high percentage of resistance to antibiotics classically considered first-line. New active antibiotics have recently been developed against Pseudomonas aeruginosa, even against multi-drug resistant strains. This review analyzes both the differential characteristics of Pseudomonas aeruginosa infections and the new therapeutic options, focusing on multi-drug resistant Pseudomonas aeruginosa.

Microbiota Assessment of Pediatric Simple and Complex Acute Appendicitis

Background and Objectives. The aim of this study is to determine the prevailing microbiota in samples from pediatric patients with acute appendicitis, as well as evaluate the antibacterial sensitivity of the isolated microorganisms, comparing the data obtained with the clinic’s antibacterial therapy guidelines. Materials and Methods. The study group consisted of 93 patients between the ages of 7 and 18. All patients underwent a laparoscopic or conventional appendectomy. The children were hospitalized with signs and symptoms suggestive of acute appendicitis. Microbiological cultures from the appendix and abdominal cavity were collected intraoperatively. Results. E. coli was identified in most cases irrespective of the clinical presentation of acute appendicitis. Most strains were susceptible to ampicillin and amoxicillin/clavulanic acid. Five strains of E. coli produced extended spectrum beta-lactamase (ESBL). Pseudomonas aeruginosa (P. aeruginosa) was the second most commonly isolated causative agent. Furthermore, it was common in cases of acute complex appendicitis. Most strains of P. aeruginosa were resistant to amoxicillin/clavulanic acid, ertapenem, ampicillin and cefotaxime, yet were susceptible to ceftazidime. Regardless of the clinical presentation, the samples yielded mixed isolates. Conclusion. E. coli is the main causative agent of acute appendicitis in the pediatric population displaying susceptibility to various antibiotics. P. aeruginosa was more prevalent in cases of acute complex appendicitis. P. aeruginosa isolates were susceptible to ceftazidime; however, they were resistant to cefotaxime, which should, therefore, be removed from guidelines for empirical antibacterial treatment of acute appendicitis due to phenotypic resistance of P. aeruginosa. We recommend antibiotics with distinct implementation to avoid antibiotic resistance.

Comparative In Vitro Activity of Ceftolozane/Tazobactam against Clinical Isolates of Pseudomonas aeruginosa and Enterobacterales from Five Latin American Countries

Background: Ceftolozane/tazobactam (C/T) is a combination of an antipseudomonal oxyiminoaminothiazolyl cephalosporin with potent in vitro activity against Pseudomonas aeruginosa and tazobactam, a known β-lactamase inhibitor. The aim of this study was to evaluate the activity of C/T against clinical isolates of P. aeruginosa and Enterobacterales collected from five Latin American countries between 2016 and 2017, before its clinical use in Latin America, and to compare it with the activity of other available broad-spectrum antimicrobial agents. Methods: a total of 2760 clinical isolates (508 P. aeruginosa and 2252 Enterobacterales) were consecutively collected from 20 hospitals and susceptibility to C/T and comparator agents was tested and interpreted following the current guidelines. Results: according to the CLSI breakpoints, 68.1% (346/508) of P. aeruginosa and 83.9% (1889/2252) of Enterobacterales isolates were susceptible to C/T. Overall, C/T demonstrated higher in vitro activity than currently available cephalosporins, piperacillin/tazobactam and carbapenems when tested against P. aeruginosa, and its performance in vitro was comparable to fosfomycin. When tested against Enterobacterales, it showed higher activity than cephalosporins and piperacillin/tazobactam, and similar activity to ertapenem. Conclusions: these results show that C/T is an active β-lactam agent against clinical isolates of P. aeruginosa and Enterobacterales.

Activity of ceftolozane/tazobactam against Gram-negative isolates among different infections in Hong Kong: SMART 2017-2019

Introduction. Ceftolozane/tazobactam was approved by the Drug Office, Department of Health, Government of the Hong Kong Special Administrative Region in 2017.Hypothesis/Gap Statement. Currently the in vitro activity of ceftolozane/tazobactam against Gram-negative pathogens isolated from patients in Hong Kong is undocumented. It would be prudent to document the activity of ceftolozane/tazobactam against Pseudomonas aeruginosa and Enterobacterales isolated from hospitalized patients in Hong Kong.Aim. To describe the in vitro susceptibility of recent clinical isolates of P. aeruginosa and the two most common Enterobacterales species (Klebsiella pneumoniae, Escherichia coli) cultured from respiratory tract, intra-abdominal, urinary tract and bloodstream infection samples to ceftolozane/tazobactam and other commonly used antimicrobial agents.Methodology. CLSI-defined broth microdilution MICs were determined and interpreted for Gram-negative isolates collected in Hong Kong from 2017 to 2019 by the SMART surveillance programme.Results. For P. aeruginosa, 96.7 % of isolates (n=210) were susceptible to ceftolozane/tazobactam, while susceptibility rates were ≥14 % lower to meropenem (82.9 % susceptible), cefepime (82.4 %), ceftazidime (81.4 %), piperacillin/tazobactam (76.7 %) and levofloxacin (79.5 %). Ceftolozane/tazobactam inhibited 85.7 % of piperacillin/tazobactam-nonsusceptible isolates, 80.6-82.1 % of cefepime-, ceftazidime- or meropenem-nonsusceptible isolates, and 75.9 % of multidrug-resistant (MDR) isolates of P. aeruginosa. For K. pneumoniae, 96.1 % of isolates (n=308) were susceptible to ceftolozane/tazobactam compared with meropenem (99.0 % susceptible), piperacillin/tazobactam (93.8 %), cefepime (85.7 %) and ceftazidime (85.4 %). The majority (88.3 %) of ESBL (extended-spectrum β-lactamase) non-CRE (carbapenem-resistant Enterobacterales) phenotype isolates of K. pneumoniae were susceptible to ceftolozane/tazobactam, comparable to piperacillin/tazobactam (85.0 %) but lower than meropenem (100 %). For E. coli, 98.5 % of isolates (n=609) were susceptible to ceftolozane/tazobactam compared to meropenem (99.3 % susceptible), piperacillin/tazobactam (96.7 %), ceftazidime (82.3 %) and cefepime (76.5 %). The majority (96.7 %) of ESBL non-CRE phenotype isolates of E. coli were susceptible to ceftolozane/tazobactam, similar to both meropenem (100 %) and piperacillin/tazobactam (94.5 %).Conclusions. Overall, >96 % of clinical isolates of P. aeruginosa, K. pneumoniae and E. coli collected in Hong Kong in 2017-2019 were susceptible to ceftolozane/tazobactam, while the activity of several commonly prescribed β-lactams was reduced, especially for P. aeruginosa. Continued surveillance of ceftolozane/tazobactam and other agents is warranted.

The Role of Colistin in the Era of New β-Lactam/β-Lactamase Inhibitor Combinations

With the current crisis related to the emergence of carbapenem-resistant Gram-negative bacteria (CR-GNB), classical treatment approaches with so-called “old-fashion antibiotics” are generally unsatisfactory. Newly approved β-lactam/β-lactamase inhibitors (BLBLIs) should be considered as the first-line treatment options for carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. However, colistin can be prescribed for uncomplicated lower urinary tract infections caused by CR-GNB by relying on its pharmacokinetic and pharmacodynamic properties. Similarly, colistin can still be regarded as an alternative therapy for infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) until new and effective agents are approved. Using colistin in combination regimens (i.e., including at least two in vitro active agents) can be considered in CRAB infections, and CRE infections with high risk of mortality. In conclusion, new BLBLIs have largely replaced colistin for the treatment of CR-GNB infections. Nevertheless, colistin may be needed for the treatment of CRAB infections and in the setting where the new BLBLIs are currently unavailable. In addition, with the advent of rapid diagnostic methods and novel antimicrobials, the application of personalized medicine has gained significant importance in the treatment of CRE infections.

Emergence of a VIM-2-producing XDR Pseudomonas aeruginosa ST309 in South America: a comparative genomic analysis

Pseudomonas aeruginosa has been considered a top priority pathogen associated with elevated morbidity and mortality. Worldwide outbreaks have been associated with few high-risk epidemic P. aeruginosa lineages. However, the biological features involved with the persistence and spread of such lineages among clinical settings remain to be unraveled. This study reports the emergence of an XDR ST309 P. aeruginosa in South America/Brazil, more precisely, in the Amazon region. Genomic analyses were performed with 42 complete and draft ST309 genomes, giving insights into its epidemiology, resistome, and mobilome. Heterogeneous distribution of acquired antimicrobial resistance genes among ST309 genomes was observed, which included bla_VIM-2, bla_IMP-15, and qnrVC1, all of them associated with class 1 integrons. The mobilome mining showed the presence of Integrative and Conjugative Elements, transposons, and genomic islands harbouring a huge arsenal of heavy metal resistance determinants, which probably provided adaptive advantages to ST309 lineage.

Real-world Performance of Susceptibility Testing for Ceftolozane/Tazobactam Against Non-Carbapenemase-Producing Carbapenem-Resistant Pseudomonas aeruginosa

Ceftolozane/tazbactam (C/T) is a potent anti-pseudomonal agent that has clinical utility against infections caused by non-carbapenemase producing carbapenem-resistant P. aeruginosa (non-CP-CR-PA). Accurate, precise and reliable antimicrobial susceptibility testing (AST) is crucial to guide clinical decisions. However, studies assessing the performance of different AST methods against non-CP-CR-PA- (the main clinical niche for C/T), are lacking. Here, we evaluated performance of gradient strips (Etest and MIC test strip (MTS), and disk diffusion (DD) using CLSI breakpoints. Additionally, we assessed the performance of DD using EUCAST breakpoints. For all susceptibility tests, we used a collection of 97 non-CP-CR-PA clinical isolates recovered from 11 Chilean hospitals. Both gradient strips and DD had acceptable performance when using CLSI breakpoints, yielding a categorical agreement (CA) of >90% and 92%, respectively. In contrast, DD using EUCAST breakpoints performed sub-optimally (CA 81%). MTS yielded a higher essential agreement (EA, >90%) than Etest (84%). Importantly, the performance of all methods varied significantly when the isolates were stratified by their degree of susceptibility to other anti-pseudomonal β-lactams. All methods had 100% CA when testing isolates that were pan-susceptible to all β-lactams (Pan-β-S). However, the CA markedly decreased when testing isolates resistant to all β-lactams (Pan-β-R). Indeed, the CA was 81% for Etest (6 errors), 78% for MTS (7 errors) and 78% and 56% for DD when using CLSI (7 errors) or EUCAST breakpoints (14 errors), respectively. Our results suggest that all manual AST methods have strikingly decreased performance in the context of Pan-β-R P. aeruginosa with potentially major clinical implications.

Ceftolozane/Tazobactam and Imipenem/Relebactam Cross-Susceptibility Among Clinical Isolates of Pseudomonas aeruginosa From Patients With Respiratory Tract Infections in ICU and Non-ICU Wards-SMART United States 2017-2019

BACKGROUND

Carbapenem-nonsusceptible and multidrug-resistant (MDR) P. aeruginosa, which are more common in patients with lower respiratory tract infections (LRTIs) and in patients in intensive care units (ICUs), pose difficult treatment challenges and may require new therapeutic options. Two β-lactam/β-lactamase inhibitor combinations, ceftolozane/tazobactam (C/T) and imipenem/relebactam (IMI/REL), are approved for treatment of hospital-acquired/ventilator-associated bacterial pneumonia.

METHODS

The Clinical and Laboratory Standards Institute-defined broth microdilution methodology was used to determine minimum inhibitory concentrations (MICs) against P. aeruginosa isolates collected from patients with LRTIs in ICUs (n = 720) and non-ICU wards (n = 914) at 26 US hospitals in 2017-2019 as part of the Study for Monitoring Antimicrobial Resistance Trends (SMART) surveillance program.

RESULTS

Susceptibility to commonly used β-lactams including carbapenems was 5-9 percentage points lower and MDR rates 7 percentage points higher among isolates from patients in ICUs than those in non-ICU wards (P < .05). C/T and IMI/REL maintained activity against 94.0% and 90.8% of ICU isolates, respectively, while susceptibility to all comparators except amikacin (96.0%) was 63%-76%. C/T and IMI/REL inhibited 83.1% and 68.1% of meropenem-nonsusceptible (n = 207) and 71.4% and 65.7% of MDR ICU isolates (n = 140), respectively. Among all ICU isolates, only 2.5% were nonsusceptible to both C/T and IMI/REL, while 6.7% were susceptible to C/T but not to IMI/REL and 3.5% were susceptible to IMI/REL but not to C/T.

CONCLUSIONS

These data suggest that susceptibility to both C/T and IMI/REL should be considered for testing at hospitals, as both agents could provide important new options for treating patients with LRTIs, especially in ICUs where collected isolates show substantially reduced susceptibility to commonly used β-lactams.