ESBLs and resistance to ceftazidime/avibactam and ceftolozane/tazobactam combinations in Escherichia coli and Pseudomonas aeruginosa

Genomic epidemiology and ceftazidime-avibactam high-level resistance mechanisms of Pseudomonas aeruginosa in China from 2010 to 2022

Ceftazidime-avibactam (CZA) resistance is a huge threat in the clinic; however, the underlying mechanism responsible for high-level CZA resistance in Pseudomonas aeruginosa (PA) isolates remains unknown. In this study, a total of 5,763 P. aeruginosa isolates were collected from 2010 to 2022 to investigate the ceftazidime-avibactam (CZA) high-level resistance mechanisms of Pseudomonas aeruginosa (PA) isolates in China. Fifty-six PER-producing isolates were identified, including 50 isolates carrying blaPER-1 in PA, and 6 isolates carrying blaPER-4. Of these, 82.1% (46/56) were classified as DTR-PA isolates, and 76.79% (43/56) were resistant to CZA. Importantly, blaPER-1 and blaPER-4 overexpression led to 16-fold and >1024-fold increases in the MICs of CZA, respectively. WGS revealed that the blaPER-1 gene was located in two different transferable IncP-2-type plasmids and chromosomes, whereas blaPER-4 was found only on chromosomes and was carried by a class 1 integron embedded in a Tn6485-like transposon. Overexpression of efflux pumps may be associated with high-level CZA resistance in blaPER-1-positive strains. Kinetic parameter analysis revealed that PER-4 exhibited a similar kcat/Km with ceftazidime and a high (∼3359-fold) IC50 value with avibactam compared to PER-1. Our study found that overexpression of PER-1 combined with enhanced efflux pump expression and the low affinity of PER-4 for avibactam contributes to high-level resistance to CZA. Additionally, the Tn6485-like transposon plays a significant role in disseminating blaPER. Urgent active surveillance is required to prevent the further spread of high-level CZA resistance in DTR-PA isolates.

Not all carbapenem-resistant Pseudomonas aeruginosa strains are alike: tailoring antibiotic therapy based on resistance mechanisms

PURPOSE OF REVIEW

To correlate the resistance mechanisms and the susceptibility to new antibiotics in Pseudomonas aeruginosa .

RECENT FINDINGS

Definition of antibiotic resistance in Pseudomonas aeruginosa is still debated. Carbapenem-resistant Pseudomonas aeruginosa (CRPA) and difficult-to-treat resistant Pseudomonas aeruginosa (DTR-PA) are used but which of them better correlate with the risk of mortality remains debated. Mechanisms underlying resistance in Pseudomonas aeruginosa are complex and may be combined, resulting in unpredictable phenotype and cross-resistance. Thus, not all CRPA are alike and tailoring antibiotic therapy on resistance mechanisms is challenging.

SUMMARY

Current guidelines recommend the use of new antipseudomonal agents for CRPA or DTR-PA infections but they don't provide specific information on how tailoring antibiotic therapy on underlying resistance mechanisms. This review may be useful to understand which mechanisms are involved in CRPA and may have practical implications helping clinicians to select an appropriate antibiotic regimen. Several antibiotics are now available for Pseudomonas aeruginosa but their rational use is important to avoid development of future resistance. The knowledge of local epidemiology and most common resistance mechanisms may guide empirical therapy, but targeted antibiotic therapy should be re-evaluated as soon as susceptibility testing profile is available and selected according to Pseudomonas aeruginosa phenotype.

Mechanisms leading to in vivo ceftazidime/avibactam resistance development during treatment of GES-5-producing Pseudomonas aeruginosa infections

The mechanisms underlying ceftazidime/avibactam resistance development in four ceftazidime/avibactam susceptible/resistant pairs of GES-5-producing ST235 Pseudomonas aeruginosa clinical isolates were investigated. In three of the cases, ceftazidime/avibactam resistance was driven by a single mutation leading to GES-27 (P162Q), GES-29 (P162A), or the novel GES-60 (N136S), as confirmed through cloning experiments. Moreover, these mutations were associated with increased cefiderocol MICs but reduced carbapenem, particularly imipenem/relebactam, resistance. Understanding the complexity of resistance mechanisms to the growing repertoire of antipseudomonal β-lactams is crucial to guide optimized treatments and antimicrobial stewardship measures.

Antimicrobial susceptibility profile of ceftolozane/tazobactam, ceftazidime/avibactam and cefiderocol against carbapenem-resistant Pseudomonas aeruginosa clinical isolates from Türkiye

PURPOSE

Carbapenem resistant Pseudomonas aeruginosa (CR-PA) is escalating worldwide and leaves clinicians few therapeutic options in recent years, β-lactam/β-lactamase inhibitor combinations (ceftolozane-tazobactam, ceftazidime-avibactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of P. aeruginosa infection and have shown potent activity against isolates defined as carbapenem resistant. The aim of this study was to determine the phenotypic profile of these agents against CR-PA in the emerging setting of carbapenemases.

METHODS

CR-PA clinical isolates were collected from three teaching hospitals in different geographical regions between January 2017-December 2021. All isolates were subjected to phenotypic carbapenemase testing using modified carbapenem inactivation method. MICs were determined by reference broth microdilution and evaluated according to EUCAST standards, while genotypic profiling was determined using PCR methods.

RESULTS

244 CR-PA sourced most frequently from the respiratory tract (32.2%), blood (20.4%) and urine (17.5%) were evaluated. Of all isolates, 32 (13.1%) were phenotypically and 38 (15.6%) were genotypically defined as carbapenemase-positive. The most common carbapenemase was GES (63.1%), followed by VIM (15.8%). The MIC50/90(S%) of ceftazidime/avibactam, ceftolozane/tazobactam and cefiderocol in all CR-PA isolates were 4 and 32 (80%), 1 and > 64 (69%) and 0.25 and 1 mg/L (96%), respectively. Cefiderocol was also the most active agent in carbapenemase-positive isolates (90%).

CONSLUSION

While ceftolozane/tazobactam and ceftazidime/avibactam remained highly active against CR-PA devoid of carbapenemases, cefiderocol provided potent in vitro activity irrespective of carbapenemase production. When considering the potential clinical utility of newer agents against CR-PA, regional variations in carbapenemase prevalence must be considered.

Phenotypic and molecular characterization of multidrug-resistant Enterobacterales isolated from clinical samples in Palestine: a focus on extended-spectrum β-lactamase- and carbapenemase-producing isolates

BACKGROUND

Infections resulting from multidrug-resistant Enterobacterales (MDR-E) pose a growing global threat, presenting challenges in treatment and contributing significantly to morbidity and mortality rates. The main objective of this study was to characterize phenotypically and genetically extended-spectrum β-lactamase- and carbapenemase- producing Enterobacterales (ESBLE and CPE respectively) isolated from clinical samples in the West Bank, Palestine.

METHODS

A cross sectional study was conducted in October 2023 on clinical bacterial isolates collected from five governmental hospitals in the West Bank, Palestine. The isolates obtained from the microbiology laboratories of the participating hospitals, underwent identification and antibiotic susceptibility testing (AST) using the VITEK® 2 Compact system. ESBL production was determined by the Vitek2 Compact system. A modified carbapenem inactivation method (mCIM) was employed to identify carbapenemase-producing Enterobacterales (CPE). Resistance genes were detected by real-time PCR.

RESULTS

Out of the total 1380 collected isolates, we randomly selected 600 isolates for analysis. Our analysis indicated that 287 (47.83%) were extended-spectrum beta-lactamase producers (ESBLE), and 102 (17%) as carbapenem-resistant Enterobacterales (CRE) isolates. A total of 424 isolates (70.67%) were identified as multidrug-resistant Enterobacterales (MDRE). The most prevalent ESBL species were K. pneumoniae (n = 124; 43.2%), E. coli (n = 119; 41.5%) and E. cloacae (n = 31; 10.8%). Among the CRE isolates, 85 (83.33%) were carbapenemase-producing Enterobacterales (CPE). The most frequent CRE species were K. pneumoniae (n = 63; 61.7%), E. coli (n = 25; 24.5%) and E. cloacae (n = 13; 12.8%). Additionally, 47 (7.83%) isolates exhibited resistance to colistin (CT), with 38 (37.62%) being CT-resistant CRE and 9 (3.14%) being CT-resistant ESBLE while sensitive to carbapenems. We noticed that 11 isolates (6 Klebsiella pneumoniae and 5 Enterobacter cloacae complex) demonstrated sensitivity to carbapenems by phenotype but carried silent CPE genes (1 blaOXA48, and 6 blaNDM, 4 blaOXA48, blaNDM). ESBL-producing Enterobacterales strains exhibited varied resistance patterns across different antibiotic classes. E. coli isolates showed notable 48% resistance to trimethoprim/sulfamethoxazole. K. pneumoniae isolates displayed a significant resistance to trimethoprim/sulfamethoxazole, nitrofurantoin, and fosfomycin (54%, 90%, and 70% respectively). E. cloacae isolates showed complete resistance to nitrofurantoin and fosfomycin. P. mirabilis isolates exhibited high resistance against fluoroquinolones (83%), and complete resistance to trimethoprim/sulfamethoxazole, nitrofurantoin and fosfomycin.

CONCLUSION

This study showed the high burden of the ESBLE and CRE among the samples collected from the participating hospitals. The most common species were K. pneumoniae and E. coli. There was a high prevalence of blaCTXm. Adopting both conventional and molecular techniques is essential for better surveillance of the emergence and spread of antimicrobial-resistant Enterobacterales infections in Palestine.

Resistance to ceftazidime-avibactam and other new β-lactams in Pseudomonas aeruginosa clinical isolates: a multi-center surveillance study

New β-lactam-β-lactamase inhibitor combinations represent last-resort antibiotics to treat infections caused by multidrug-resistant Pseudomonas aeruginosa. Carbapenemase gene acquisition can limit their spectrum of activity, and reports of resistance toward these new molecules are increasing. In this multi-center study, we evaluated the prevalence of resistance to ceftazidime-avibactam (CZA) and comparators among P. aeruginosa clinical isolates from bloodstream infections, hospital-acquired or ventilator-associated pneumonia, and urinary tract infections, circulating in Southern Italy. We also investigated the clonality and content of relevant β-lactam resistance mechanisms of CZA-resistant (CZAR) isolates. A total of 120 P. aeruginosa isolates were collected. CZA was among the most active β-lactams, retaining susceptibility in the 81.7% of cases, preceded by cefiderocol (95.8%) and followed by ceftolozane-tazobactam (79.2%), meropenem-vaborbactam (76.1%), imipenem-relebactam (75%), and aztreonam (69.6%). Among non-β-lactams, colistin and amikacin were active against 100% and 85.8% of isolates respectively. In CZAR strains subjected to whole-genome sequencing (n = 18), resistance was mainly due to the expression of metallo-β-lactamases (66.6% VIM-type and 5.5% FIM-1), followed by PER-1 (16.6%) and GES-1 (5.5%) extended-spectrum β-lactamases, mostly carried by international high-risk clones (ST111 and ST235). Of note, two strains producing the PER-1 enzyme were resistant to all β-lactams, including cefiderocol. In conclusion, the CZA resistance rate among P. aeruginosa clinical isolates in Southern Italy remained low. CZAR isolates were mostly metallo-β-lactamases producers and belonging to ST111 and ST253 epidemic clones. It is important to implement robust surveillance systems to monitor emergence of new resistance mechanisms and to limit the spread of P. aeruginosa high-risk clones.

IMPORTANCE

Multidrug-resistant Pseudomonas aeruginosa infections are a growing threat due to the limited therapeutic options available. Ceftazidime-avibactam (CZA) is among the last-resort antibiotics for the treatment of difficult-to-treat P. aeruginosa infections, although resistance due to the acquisition of transferable β-lactamase genes is increasing. With this work, we report that CZA represents a highly active antipseudomonal β-lactam compound (after cefiderocol), and that metallo-β-lactamases (VIM-type) and extended-spectrum β-lactamases (GES and PER-type) production is the major factor underlying CZA resistance in isolates from Southern Italian hospitals. In addition, we reported that such resistance mechanisms were mainly carried by the international high-risk clones ST111 and ST235.

Non-KPC Attributes of Newer β-lactam/β-lactamase Inhibitors, Part 1: Enterobacterales and Pseudomonas aeruginosa

Gram-negative antibiotic resistance continues to grow as a global problem due to the evolution and spread of β-lactamases. The early β-lactamase inhibitors (BLIs) are characterized by spectra limited to class A β-lactamases and ineffective against carbapenemases and most extended spectrum β-lactamases. In order to address this therapeutic need, newer BLIs were developed with the goal of treating carbapenemase producing, carbapenem resistant organisms (CRO), specifically targeting the Klebsiella pneumoniae carbapenemase (KPC). These BL/BLI combination drugs, avibactam/avibactam, meropenem/vaborbactam, and imipenem/relebactam, have proven to be indispensable tools in this effort. However, non-KPC mechanisms of resistance are rising in prevalence and increasingly challenging to treat. It is critical for clinicians to understand the unique spectra of these BL/BLIs with respect to non-KPC CRO. In Part 1of this 2-part series, we describe the non-KPC attributes of the newer BL/BLIs with a focus on utility against Enterobacterales and Pseudomonas aeruginosa.

The individual contributions of blaB, blaGOB and blaCME on MICs of β-lactams in Elizabethkingia anophelis

BACKGROUND

The blaB, blaGOB and blaCME genes are thought to confer β-lactam resistance to Elizabethkingia anophelis, based on experiments conducted primarily on Escherichia coli.

OBJECTIVES

To determine the individual contributions of β-lactamase genes to increased MICs in E. anophelis and to assess their impact on the in vivo efficacy of carbapenem therapy.

METHODS

Scarless gene deletion of one or more β-lactamase gene(s) was performed in three clinical E. anophelis isolates. MICs were determined by broth microdilution. Hydrolytic activity and expressions of β-lactamase genes were measured by an enzymatic assay and quantitative RT-PCR, respectively. In vivo efficacy was determined using Galleria mellonella and murine thigh infection models.

RESULTS

The presence of blaB resulted in >16-fold increases, while blaGOB caused 4-16-fold increases of carbapenem MICs. Hydrolysis of carbapenems was highest in lysates of blaB-positive strains, possibly due to the constitutionally higher expression of blaB. Imipenem was ineffective against blaB-positive isolates in vivo in terms of improvement of the survival of wax moth larvae and reduction of murine bacterial load. The deletion of blaB restored the efficacy of imipenem. The blaB gene was also responsible for a >4-fold increase of ampicillin/sulbactam and piperacillin/tazobactam MICs. The presence of blaCME, but not blaB or blaGOB, increased the MICs of ceftazidime and cefepime by 8-16- and 4-8-fold, respectively.

CONCLUSIONS

The constitutionally and highly expressed blaB gene in E. anophelis was responsible for increased MICs of carbapenems and led to their poor in vivo efficacy. blaCME increased the MICs of ceftazidime and cefepime.

Ceftazidime/avibactam resistance is associated with PER-3-producing ST309 lineage in Chilean clinical isolates of non-carbapenemase producing Pseudomonas aeruginosa

Introduction

Ceftazidime/avibactam (CZA) is indicated against multidrug-resistant Pseudomonas aeruginosa, particularly those that are carbapenem resistant. CZA resistance in P. aeruginosa producing PER, a class A extended-spectrum β-lactamase, has been well documented in vitro. However, data regarding clinical isolates are scarce. Our aim was to analyze the contribution of PER to CZA resistance in non-carbapenemase-producing P. aeruginosa clinical isolates that were ceftazidime and/or carbapenem non-susceptible.

Methods

Antimicrobial susceptibility was determined through agar dilution and broth microdilution, while bla PER gene was screened through PCR. All PER-positive isolates and five PER-negative isolates were analyzed through Whole Genome Sequencing. The mutational resistome associated to CZA resistance was determined through sequence analysis of genes coding for PBPs 1b, 3 and 4, MexAB-OprM regulators MexZ, MexR, NalC and NalD, AmpC regulators AmpD and AmpR, and OprD porin. Loss of bla PER-3 gene was induced in a PER-positive isolate by successive passages at 43°C without antibiotics.

Results

Twenty-six of 287 isolates studied (9.1%) were CZA-resistant. Thirteen of 26 CZA-resistant isolates (50%) carried bla PER. One isolate carried bla PER but was CZA-susceptible. PER-producing isolates had significantly higher MICs for CZA, amikacin, gentamicin, ceftazidime, meropenem and ciprofloxacin than non-PER-producing isolates. All PER-producing isolates were ST309 and their bla PER-3 gene was associated to ISCR1, an insertion sequence known to mobilize adjacent DNA. PER-negative isolates were classified as ST41, ST235 (two isolates), ST395 and ST253. PER-negative isolates carried genes for narrow-spectrum β-lactamases and the mutational resistome showed that all isolates had one major alteration in at least one of the genes analyzed. Loss of bla PER-3 gene restored susceptibility to CZA, ceftolozane/tazobactam and other β-lactamsin the in vitro evolved isolate.

Discussion

PER-3-producing ST309 P. aeruginosa is a successful multidrug-resistant clone with blaPER-3 gene implicated in resistance to CZA and other β-lactams.

The Prevalence of Antibiotic Resistance Phenotypes and Genotypes in Multidrug-Resistant Bacterial Isolates from the Academic Hospital of Jaén, Spain

The heterogenicity of antimicrobial resistance genes described in clinically significant bacterial isolates and their potential role in reducing the efficacy of classically effective antibiotics pose a major challenge for global healthcare, especially in infections caused by Gram-negative bacteria. We analyzed 112 multidrug-resistant (MDR) isolates from clinical samples in order to detect high resistance profiles, both phenotypically and genotypically, among four Gram-negative genera (Acinetobacter, Escherichia, Klebsiella, and Pseudomonas). We found that 9.8% of the total selected isolates were classified as extensively drug-resistant (XDR) (six isolates identified as A. baumannii and five among P. pneumoniae isolates). All other isolates were classified as MDR. Almost 100% of the isolates showed positive results for blaOXA-23 and blaNDM-1 genes among the A. baumannii samples, one resistance gene (blaCTX-M) among E. coli, and two genetic determinants (blaCTX-M and aac(6')-Ib) among Klebsiella. In contrast, P. aeruginosa showed just one high-frequency antibiotic resistance gene (dfrA), which was present in 68.42% of the isolates studied. We also describe positive associations between ampicillin and cefotaxime resistance in A. baumannii and the presence of blaVEB and blaGES genes, as well as between the aztreonam resistance phenotype and the presence of blaGES gene in E. coli. These data may be useful in achieving a better control of infection strategies and antibiotic management in clinical scenarios where these multidrug-resistant Gram-negative pathogens cause higher morbidity and mortality.

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.

Comparison of three doses of amikacin on alternate days with a daily dose of meropenem during the same period for the treatment of urinary tract infection with E. coli: a double-blind clinical trial

OBJECTIVES

Urinary tract infections (UTIs) are very common infections in humans, and Escherichia coli (E. coli) is the commonest pathogen leading to UTIs. The generation of beta-lactamase enzymes in this bacterium results in its resistance against many antibiotics. This study compares three doses of amikacin on alternate days with a daily dose of meropenem in the same period for the treatment of UTIs with E. coli in a double-blind clinical trial.

METHODS

The current double-blind clinical trial compares three doses of amikacin on alternate days with a daily dose of meropenem in the same period for the treatment of UTIs with E. coli. The patients were assigned to two groups: Intervention (receiving a single dose of amikacin once a day at 48-h intervals for a week, three doses) and control (receiving meropenem for 1/TDS for a week).

RESULTS

The E. coli infection frequency was 61 (21 cases of non-ESBL and 40 cases of ESBL-positive infections) and the frequency of the other infections was 52 (46%). In the patients with ESBL E. coli infection, ciprofloxacin (21; 70%) showed the highest antibiotic resistance, and nitrofurantoin (33; 91.7%) showed the highest sensitivity. The baseline variables between the control and intervention groups indicated no significant difference (p > 0.05). The frequency of signs and symptoms showed no significant difference between the amikacin and meropenem groups in the first 24 h and the first week. In the second week of follow-up, no clinical signs or symptoms were observed in the two groups.

CONCLUSION

The results of this study showed that treatment with amikacin, 1 g q48h, for one week (three doses) has the same result as meropenem, 1 g q8h, for one week (21 doses). The results are the same for the treatment of UTIs with ESBL positive and ESBL negative. Amikacin can be used once every 48 h to treat UTIs, is less expensive and can be administered on an outpatient basis.

TRIAL REGISTRATION

This study was registered in the Iranian Registry of Clinical Trials (IRCT) with ID number: IRCT20170417033483N2 on the date 2018-02-13.

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.

Resistance in Pseudomonas aeruginosa: A Narrative Review of Antibiogram Interpretation and Emerging Treatments

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium renowned for its resilience and adaptability across diverse environments, including clinical settings, where it emerges as a formidable pathogen. Notorious for causing nosocomial infections, P. aeruginosa presents a significant challenge due to its intrinsic and acquired resistance mechanisms. This comprehensive review aims to delve into the intricate resistance mechanisms employed by P. aeruginosa and to discern how these mechanisms can be inferred by analyzing sensitivity patterns displayed in antibiograms, emphasizing the complexities encountered in clinical management. Traditional monotherapies are increasingly overshadowed by the emergence of multidrug-resistant strains, necessitating a paradigm shift towards innovative combination therapies and the exploration of novel antibiotics. The review accentuates the critical role of accurate antibiogram interpretation in guiding judicious antibiotic use, optimizing therapeutic outcomes, and mitigating the propagation of antibiotic resistance. Misinterpretations, it cautions, can inadvertently foster resistance, jeopardizing patient health and amplifying global antibiotic resistance challenges. This paper advocates for enhanced clinician proficiency in interpreting antibiograms, facilitating informed and strategic antibiotic deployment, thereby improving patient prognosis and contributing to global antibiotic stewardship efforts.

Impact of Acquired Broad Spectrum β-Lactamases on Susceptibility to Novel Combinations Made of β-Lactams (Aztreonam, Cefepime, Meropenem, and Imipenem) and Novel β-Lactamase Inhibitors in Escherichia coli and Pseudomonas aeruginosa

The impact of broad-spectrum β-lactamases on the susceptibility to novel β-lactamase/β-lactamase inhibitor combinations was evaluated both in Pseudomonas aeruginosa and Escherichia coli using isogenic backgrounds. Cefepime-zidebactam displayed low MICs, mainly due to the significant intrinsic antibacterial activity of zidebactam. Cefepime-taniborbactam showed excellent activity against recombinant E. coli strains, including metallo-β-lactamase producers, whereas aztreonam-avibactam remained the best therapeutic option against class B β-lactamase-producing P. aeruginosa.

Assessing the in vivo efficacy of rational antibiotics and combinations against difficult-to-treat Pseudomonas aeruginosa producing GES β-lactamases

OBJECTIVES

We evaluated the in vivo efficacy of human-simulated regimens (HSRs) of cefiderocol, ceftazidime/avibactam, meropenem and ceftazidime/avibactam/meropenem combination against Guiana-extended spectrum (GES)-producing Pseudomonas aeruginosa isolates.

METHODS

Eighteen P. aeruginosa isolates producing GES-1 (n = 5), GES-5 (n = 5) or miscellaneous GESs (combinations of GES-19, GES-20 and/or GES-26; n = 8) were evaluated. In vitro MIC testing was determined using broth microdilution. In a validated murine thigh infection model, HSRs of cefiderocol 2 g q8h as a 3 h IV infusion, ceftazidime/avibactam 2.5 g q8h as a 2 h IV infusion, meropenem 2 g q8h as a 3 h IV infusion or ceftazidime/avibactam/meropenem were administered. Change in bacterial burden relative to baseline and the proportion of isolates in each genotypic group meeting 1-log10 kill endpoint were assessed.

RESULTS

Modal MICs (mg/L) ranged from 0.125 to 1 for cefiderocol, 4 to >64 for ceftazidime/avibactam and 2 to >64 for meropenem. Cefiderocol produced >1-log10 of kill against all 18 tested isolates. Meropenem was active against all GES-1 isolates whereas activity against GES-5 and miscellaneous GESs was lacking, consistent with the MICs. Ceftazidime/avibactam was active against all GES-1 and GES-5 isolates and retained activity against 62.5% of miscellaneous GESs including isolates with elevated MICs. For isolates where ceftazidime/avibactam failed, the addition of meropenem restored the in vivo efficacy.

CONCLUSIONS

As monotherapy, cefiderocol was active in vivo against all tested isolates. The activities of meropenem or ceftazidime/avibactam alone were variable; however, a combination of both was active against all isolates. Cefiderocol and ceftazidime/avibactam/meropenem could be valuable therapeutic options for GES-producing P. aeruginosa infections. Clinical confirmatory data are warranted.

Insertion of ISPa1635 in ISCR1 Creates a Hybrid Promoter for blaPER-1 Resulting in Resistance to Novel β-lactam/β-lactamase Inhibitor Combinations and Cefiderocol

Eleven blaPER-1-positive Pseudomonas aeruginosa clinical isolates showed variable susceptibility to ceftazidime-avibactam (CZA). The genetic contexts of blaPER-1 were identical (ISCR1-blaPER-1-gst) except for the ST697 isolate HS204 (ISCR1-ISPa1635-blaPER-1-gst). The insertion of ISPa1635 in ISCR1 upstream of blaPER-1 created a hybrid promoter, which elevated the blaPER-1 transcription level and resulted in increased resistance to CZA, ceftolozane-tazobactam, cefepime-zidebactam, and cefiderocol. Diversity in the promoter activity of blaPER-1 partially explains the variable susceptibility to CZA in PER-producing isolates.

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.

Multifactorial resistance mechanisms associated with resistance to ceftazidime-avibactam in clinical Pseudomonas aeruginosa isolates from Switzerland

Background

Increasing reports of multidrug resistance (MDR) in clinical Pseudomonas aeruginosa have led to a necessity for new antimicrobials. Ceftazidime-avibactam (CZA) is indicated for use against MDR P. aeruginosa across a broad range of infection types and particularly those that are carbapenem resistant. This study sought to determine the molecular mechanisms of CZA and imipenem (IPM)-resistance in clinical P. aeruginosa isolates obtained from Swiss hospitals.

Methods

Clinical P. aeruginosa isolates were obtained from inpatients in three hospitals in Switzerland. Susceptibility was determined by either antibiotic disc testing or broth microdilution according to EUCAST methodology. AmpC activity was determined using cloxacillin and efflux activity was determined using phenylalanine-arginine β-naphthylamide, in agar plates. Whole Genome Sequencing was performed on 18 clinical isolates. Sequence types (STs) and resistance genes were ascertained using the Centre for Genomic Epidemiology platform. Genes of interest were extracted from sequenced isolates and compared to reference strain P. aeruginosa PAO1.

Results

Sixteen different STs were identified amongst the 18 isolates in this study indicating a high degree of genomic diversity. No carbapenemases were detected but one isolate did harbor the ESBL bla PER-1. Eight isolates were CZA-resistant with MICs ranging from 16-64 mg/L, and the remaining ten isolates had either low/wildtype MICs (n=6; 1-2 mg/L) or elevated, but still susceptible, MICs (n=4; 4-8 mg/L). Ten isolates were IPM-resistant, seven of which had mutations resulting in truncations of OprD, and the remaining nine IPM-susceptible isolates had intact oprD genes. Within CZA-R isolates, and those with reduced susceptibility, mutations resulting in ampC derepression, OprD loss, mexAB overexpression and ESBL (bla PER-1) carriage were observed in various combinations and one harbored a truncation of the PBP4 dacB gene. Within the six isolates with wildtype-resistance levels, five had no mutations that would affect any antimicrobial resistance (AMR) genes of interest when compared to PAO1.

Conclusion

This preliminary study highlights that CZA-resistance in P. aeruginosa is multifactorial and could be caused by the interplay between different resistance mechanisms including ESBL carriage, increased efflux, loss of permeability and derepression of its intrinsic ampC.

Molecular Mechanisms of Resistance to Ceftazidime/Avibactam in Clinical Isolates of Enterobacterales and Pseudomonas aeruginosa in Latin American Hospitals

Ceftazidime-avibactam (CZA) is the combination of a third-generation cephalosporin and a new non-β-lactam β-lactamase inhibitor capable of inactivating class A, C, and some D β-lactamases. From a collection of 2,727 clinical isolates of Enterobacterales (n = 2,235) and P. aeruginosa (n = 492) that were collected between 2016 and 2017 from five Latin American countries, we investigated the molecular resistance mechanisms to CZA of 127 (18/2,235 [0.8%] Enterobacterales and 109/492 [22.1%] P. aeruginosa). First, by qPCR for the presence of genes encoding KPC, NDM, VIM, IMP, OXA-48-like, and SPM-1 carbapenemases, and second, by whole-genome sequencing (WGS). From the CZA-resistant isolates, MBL-encoding genes were detected in all 18 Enterobacterales and 42/109 P. aeruginosa isolates, explaining their resistant phenotype. Resistant isolates that yielded a negative qPCR result for any of the MBL encoding genes were subjected to WGS. The WGS analysis of the 67 remaining P. aeruginosa isolates showed mutations in genes previously associated with reduced susceptibility to CZA, such as those involved in the MexAB-OprM efflux pump and AmpC (PDC) hyperproduction, PoxB (bla_OXA-50-like), FtsI (PBP3), DacB (PBP4), and OprD. The results presented here offer a snapshot of the molecular epidemiological landscape for CZA resistance before the introduction of this antibiotic into the Latin American market. Therefore, these results serve as a valuable comparison tool to trace the evolution of the resistance to CZA in this carbapenemase-endemic geographical region. IMPORTANCE In this manuscript, we determine the molecular mechanisms of ceftazidime-avibactam resistance in Enterobacterales and P. aeruginosa isolates from five Latin American countries. Our results reveal a low rate of resistance to ceftazidime-avibactam among Enterobacterales; in contrast, resistance in P. aeruginosa has proven to be more complex, as it might involve multiple known and possibly unknown resistance mechanisms.

Novel Resistance Regions Carrying TnaphA6, blaVIM-2, and blaPER-1, Embedded in an ISPa40-Derived Transposon from Two Multi-Resistant Pseudomonas aeruginosa Clinical Isolates

Antibiotic resistance is an alarming problem throughout the world and carbapenem-resistant Pseudomonas aeruginosa has been cataloged as critical in the World Health Organization list of microorganisms in urgent need for the development of new antimicrobials. In this work, we describe two novel resistance regions responsible for conferring a multidrug resistance phenotype to two clinical isolates of P. aeruginosa (Pa873 and Pa6415) obtained from patients hospitalized in the ICU of University Hospital of Uruguay. Bacterial identification and antibiotic susceptibility tests were performed using MALDI-TOF and the Vitek 2 system, respectively. WGS was performed for both isolates using Oxford Nanopore Technologies and Illumina and processed by means of hybrid assembly. Both isolates were resistant to ceftazidime, cefepime, piperacillin-tazobactam, aztreonam, and imipenem. Strain Pa6415 also showed resistance to ciprofloxacin. Both strains displayed MICs below the susceptibility breakpoint for CAZ-AVI plus 4 mg/L of aztreonam as well as cefiderocol. Both resistance regions are flanked by the left and right inverted repeats of ISPa40 in two small regions spanning 39.3 and 35.6 kb, for Pa6415 and Pa873, respectively. The resistance region of Pa6415 includes TnaphA6, and the new Tn7516 consists of IRi, In899, qacEΔ1-sul1-ISCR1, qnrVC6-ISCR1-bla_PER-1-qacEΔ1-sul1, araJ-like, IS481-like tnpA, ISPa17, and IRR. On the other hand, the resistance region of Pa873 includes Tnaph6 and the new Tn7517 (IRi, In899, qacEΔ1-sul1, ISCR1-bla_PER-1-qacEΔ1-sul1, araJ-like, IS481-like tnpA, ISPa17, and IRR). It is necessary to monitor the emergence of genetic structures that threaten to invalidate the available therapeutic resources.

Antimicrobial stewardship programs in the Intensive Care Unit in patients with infections caused by multidrug-resistant Gram-negative bacilli

Antimicrobial stewardship programs (ASPs) have been shown to be effective and safe, contributing to reducing and adjusting antimicrobial use in clinical practice. Such programs not only reduce antibiotic selection pressure and therefore the selection of multidrug-resistant strains, but also reduce the potential deleterious effects for individual patients and even improve the prognosis by adjusting the choice of drug and dosage, and lessening the risk of adverse effects and interactions. Gram-negative bacilli (GNB), particularly multidrug-resistant strains (MDR-GNB), represent the main infectious problem in the Intensive Care Unit (ICU), and are therefore a target for ASPs. The present review provides an update on the relationship between ASPs and MDR-GNB.

Biochemical and molecular mechanisms of antibiotic resistance in Salmonella spp

Salmonella is a diverse Gram-negative bacterium that represents the major disease burden worldwide. According to WHO, Salmonella is one of the fourth global causes of diarrhoeal disease. Antibiotic resistance is a worldwide health concern, and Salmonella spp. is one of the microorganisms that can evade the toxicity of antimicrobials via antibiotic resistance. This review aims to deliver in-depth knowledge of the molecular mechanisms and the underlying biochemical alterations perceived in antibiotic resistance in Salmonella. This information will help understand and mitigate the impact of antibiotic-resistant bacteria on humans and contribute to the state-of-the-art research developing newer and more potent antibiotics.

In vitro activity of aztreonam in combination with newly developed β-lactamase inhibitors against MDR Enterobacterales and Pseudomonas aeruginosa producing metallo-β-lactamases

OBJECTIVES

To evaluate the in vitro activity of aztreonam in combination with novel β-lactamase inhibitors, namely avibactam, nacubactam, taniborbactam and zidebactam, against MDR MBL-producing Enterobacterales and Pseudomonas aeruginosa clinical isolates.

METHODS

MIC values of aztreonam, aztreonam/β-lactam inhibitor but also cefiderocol as comparator were determined for 64 and 39 clinical Enterobacterales or P. aeruginosa isolates, respectively, producing representative MBLs, i.e. derivatives of NDM (n = 64), VIM (n = 32), IMP (n = 8) and SPM (n = 2). MICs were also determined for Escherichia coli TOP10 and P. aeruginosa PAO1 harbouring recombinant plasmids producing the different β-lactamases under isogenic backgrounds (n = 22 and n = 11, respectively). Fifty percent inhibitory concentrations were additionally determined for the abovementioned β-lactamase inhibitors using β-lactamase crude extracts.

RESULTS

The susceptibility rate for aztreonam was 17.1% among MBL-producing Enterobacterales, while it was very high with aztreonam/zidebactam (98.4%), and to a lower extent with aztreonam/nacubactam (84.4%) and aztreonam/taniborbactam (75%), compared with aztreonam/avibactam (70.3%) and cefiderocol (39.1%). Among MBL-producing P. aeruginosa isolates, the susceptibility rates were 53.8% with aztreonam, 66.7% with aztreonam/nacubactam and aztreonam/taniborbactam combinations, and 69.2% with aztreonam/avibactam, aztreonam/zidebactam and cefiderocol.

CONCLUSIONS

Altogether, these results showed that combinations including aztreonam and novel β-lactamase inhibitors, such as zidebactam, nacubactam or taniborbactam, have a very significant in vitro activity against MDR MBL-producing Enterobacterales clinical isolates, the aztreonam/zidebactam combination being the best option. On the other hand, aztreonam/zidebactam is equivalent to aztreonam/avibactam and cefiderocol among MBL-producing P. aeruginosa isolates.

Phenotypic and genotypic profile of ceftolozane/tazobactam-non-susceptible, carbapenem-resistant Pseudomonas aeruginosa

OBJECTIVES

To evaluate the genotypic and ceftazidime/avibactam-susceptibility profiles amongst ceftolozane/tazobactam-non-susceptible (NS), MBL-negative Pseudomonas aeruginosa in a global surveillance programme.

METHODS

Isolates were collected as part of the ERACE-PA Global Surveillance programme. Carbapenem-resistant P. aeruginosa deemed clinically relevant by the submitting laboratories were included. Broth microdilution MICs were conducted per CLSI standards to ceftolozane/tazobactam, ceftazidime/avibactam, ceftazidime and cefepime. Genotypic carbapenemases were detected using CarbaR and CarbaR NxG (research use only). Isolates negative for carbapenemases by PCR were assessed via WGS. Isolates were included in the analysis if they were ceftolozane/tazobactam-NS and lacked detection of known MBLs.

RESULTS

Of the 807 isolates collected in the ERACE-PA programme, 126 (16%) were ceftolozane/tazobactam-NS and lacked MBLs. Cross-resistance to ceftazidime and cefepime was common, with only 5% and 16% testing susceptible, respectively. Ceftazidime/avibactam retained in vitro activity, with 65% of isolates testing susceptible. GES was the most common enzymology, detected in 57 (45%) isolates, and 89% remained susceptible to ceftazidime/avibactam. Seven isolates harboured KPC and all tested susceptible to ceftazidime/avibactam. In the remaining 62 isolates, WGS revealed various ESBLs or OXA β-lactamases. While 39% remained susceptible to ceftazidime/avibactam, marked variability was observed among the diverse resistance mechanisms.

CONCLUSIONS

Ceftazidime/avibactam remained active in vitro against the majority of ceftolozane/tazobactam-NS, MBL-negative P. aeruginosa. Ceftazidime/avibactam was highly active against isolates harbouring GES and KPC β-lactamases. These data highlight the potential clinical utility of genotypic profiling as well as the need to test multiple novel agents when carbapenem-resistant P. aeruginosa are encountered.

Cefiderocol against Multi-Drug and Extensively Drug-Resistant Escherichia coli: An In Vitro Study in Poland

Cefiderocol (CFDC) is a novel, broad-spectrum siderophore cephalosporin with potential activity against multi-drug (MDR) and extensively drug-resistant (XDR) Enterobacterales, including carbapenem-resistant strains. We assessed the in vitro susceptibility to CFDC of MDR, and XDR E. coli isolates derived from clinical samples of hospitalized patients. Disk diffusion (DD) and MIC (minimum inhibitory concentration) test strip (MTS) methods were used. The results were interpreted based on EUCAST (version 12.0 2022) recommendations. Among all E. coli isolates, 98 (94.2%) and 99 (95.2%) were susceptible to CFDC when the DD and MTS methods were used, respectively (MIC range: <0.016−4 µg/mL, MIC50: 0.19 µg/mL, MIC90: 0.75 µg/mL). With the DD and MTS methods, all (MIC range: 0.016−2 µg/mL, MIC50: 0.19 µg/mL, MIC90: 0.75 µg/mL) but three (96.6%) ESBL-positive isolates were susceptible to CFDC. Out of all the metallo-beta-lactamase-positive E. coli isolates (MIC range: 0.016−4 µg/mL, MIC50: 0.5 µg/mL, MIC90: 1.5 µg/mL), 16.7% were resistant to CFDC with the DD method, while 11.1% were resistant to CFDC when the MTS method was used. CFDC is a novel therapeutic option against MDR and XDR E. coli isolates and is promising in the treatment of carbapenem-resistant E. coli strains, also for those carrying Verona integron-encoded metallo-beta-lactamases, when new beta-lactam-beta-lactamase inhibitors cannot be used.

Detecting KPC-2 and NDM-1 Coexpression in Klebsiella pneumoniae Complex from Human and Animal Hosts in South America

Reports of Gram-negative bacteria harboring multiple carbapenemase genes have increased in South America, leading to an urgent need for appropriate microbiological diagnosis. We evaluated phenotypic methods for detecting Klebsiella pneumoniae carbapenemase 2 (KPC-2) and New Delhi metallo-β-lactamase-1 (NDM-1) coexpression in members of the K. pneumoniae complex (i.e., K. pneumoniae, K. quasipneumoniae, and K. variicola) isolated from human and animal hosts, based on inhibition of ceftazidime-avibactam (CZA) and aztreonam (ATM) by dipicolinic acid (DPA), EDTA, or avibactam (AVI). While the presence of blaKPC-2 and blaNDM-1 genes was confirmed by whole-genome sequencing, PCR, and/or GeneXpert, coexpression was successfully detected based on the following: (i) a ≥5-mm increase in the zone diameter of ATM (30 µg) disks plus AVI (4 or 20 µg) and ≥4-mm and ≥10-mm increases in the zone diameters for "CZA 50" (30 µg ceftazidime [CAZ] and 20 µg AVI) and "CZA 14" (10 µg CAZ and 4 µg AVI) disks, respectively, when we added DPA (1 mg/disk) or EDTA (5 mM) in a combined disk test (CDT); (ii) a positive ghost zone (synergism) between ATM (30 µg) and CZA 50 disks and between CZA 50 and DPA (1 mg) disks, using the double-disk synergy test (DDST) at a disk-disk distance of 2.5 cm; (iii) ≥3-fold MIC reductions of ATM and CZA in the presence of AVI (4 µg/mL), DPA (500 µg/mL), or EDTA (320 µg/mL); and (iv) immunochromatography. Although our results demonstrated that inhibition by AVI, DPA, and EDTA may provide simple and inexpensive methods for the presumptive detection of coexpression of KPC-2 and NDM-1 in members of the K. pneumoniae complex, additional studies are necessary to confirm the accuracy of these methodologies by testing other Gram-negative bacterial species and other KPC and NDM variants coexpressed by WHO critical priority pathogens detected worldwide. IMPORTANCE Alerts regarding the emergence and increase of combinations of carbapenemases in Enterobacterales in Latin America and the Caribbean have recently been issued by PAHO and WHO, emphasizing the importance of appropriate microbiological diagnosis and the effective and articulated implementation of infection prevention and control programs. In this study, we evaluated methods based on inhibition of ceftazidime (CAZ), ceftazidime-avibactam (CZA), and aztreonam (ATM) by dipicolinic acid (DPA), EDTA, and avibactam (AVI) inhibitors for the identification of KPC-2- and NDM-1-coexpression in members of the K. pneumoniae complex recovered from human and animal hosts. Our results demonstrate that inhibition by AVI, DPA, and EDTA may provide simple and inexpensive methods for the presumptive detection of coexpression of KPC-2 and NDM-1 in members of the K. pneumoniae complex.

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.

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.

NDM-35-Producing ST167 Escherichia coli Highly Resistant to β-Lactams Including Cefiderocol

A multidrug-resistant (carbapenems, aztreonam + avibactam, and cefiderocol) ST167 Escherichia coli clinical isolate recovered from a patient hospitalized in Switzerland produced NDM-35 showing ca. 10-fold increased hydrolytic activity toward cefiderocol compared to NDM-1. The isolate co-produced a CMY-type β-lactamase, exhibited a four amino-acid insertion in PBP3, and possessed a truncated iron transporter CirA protein. Our study identified an association of unrelated resistance mechanisms leading to resistance to virtually all β-lactams in a high-risk E. coli clone.

Treatment of carbapenem-resistant Pseudomonas aeruginosa infections: a case for cefiderocol

INTRODUCTION

Carbapenem-resistant (CR) Pseudomonas aeruginosa infections constitute a serious clinical threat globally. Patients are often critically ill and/or immunocompromised. Antibiotic options are limited and are currently centered on beta-lactam-beta-lactamase inhibitor (BL-BLI) combinations and the siderophore cephalosporin cefiderocol.

AREAS COVERED

This article reviews the mechanisms of P. aeruginosa resistance and their potential impact on the activity of current treatment options, along with evidence for the clinical efficacy of BL-BLI combinations in P. aeruginosa infections, some of which specifically target infections due to CR organisms. The preclinical and clinical evidence supporting cefiderocol as a treatment option for P. aeruginosa involving infections is also reviewed.

EXPERT OPINION

Cefiderocol is active against most known P. aeruginosa mechanisms mediating carbapenem resistance. It is stable against different serine- and metallo-beta-lactamases, and, due to its iron channel-dependent uptake mechanism, is not impacted by porin channel loss. Furthermore, the periplasmic level of cefiderocol is not affected by upregulated efflux pumps. The potential for on-treatment resistance development currently appears to be low, although more clinical data are required. Information from surveillance programs, real-world compassionate use, and clinical studies demonstrate that cefiderocol is an important treatment option for CR P. aeruginosa infections.

In vivo translational assessment of the GES genotype on the killing profile of ceftazidime, ceftazidime/avibactam and meropenem against Pseudomonas aeruginosa

Objectives

To evaluate the in vivo killing profile of human-simulated exposures of ceftazidime, ceftazidime/avibactam and meropenem against GES-harbouring Pseudomonas aeruginosa in the murine thigh infection model.

Methods

Five P. aeruginosa isolates [three isogenic (GES-1, GES-5 and GES-15) and two clinical (GES-5 and GES-15)] were evaluated. MICs were determined using broth microdilution. Human-simulated regimens (HSRs) of ceftazidime 2 g IV q8h as a 2 h infusion, ceftazidime/avibactam 2.5 g IV q8h as a 2 h infusion and meropenem 2 g IV q8h as a 3 h infusion were administered. Change in bacterial burden relative to baseline was assessed.

Results

Modal MICs ranged from 8 to >64 mg/L for ceftazidime, from 1 to 16 mg/L for ceftazidime/avibactam and from 1 to >64 mg/L for meropenem. In vivo, for the isogenic strains, avibactam augmented ceftazidime activity against the GES-1- and GES-15-harbouring isolates. Both ceftazidime and ceftazidime/avibactam resulted in significant kill against the GES-5 isogenic isolate. The meropenem HSR produced >1 log₁₀ kill against each isogenic isolate (MICs of 1–4 mg/L). Against the GES-5 clinical isolate, ceftazidime and ceftazidime/avibactam resulted in >1 log₁₀ kill compared with bacterial growth with the meropenem HSR. In the clinical isolate harbouring GES-15, the elevated MICs of ceftazidime and ceftazidime/avibactam reduced the effectiveness of both compounds, while the observed reduction in meropenem MIC translated into in vivo efficacy of the HSR regimen, predictive of clinical efficacy.

Conclusions

In GES-harbouring P. aeruginosa, quantitative reductions in bacterial density observed with the translational murine model suggest that the phenotypic profile of ceftazidime, ceftazidime/avibactam and meropenem is predictive of clinical efficacy when using the evaluated dosing regimens.

Clinical and microbiological features of ceftolozane/tazobactam resistant Pseudomonas aeruginosa isolates in a university hospital in central Italy

OBJECTIVES

Ceftolozane/tazobactam (C/T) is a novel cephalosporin and β-lactamase inhibitor combination with great activity against Pseudomonas aeruginosa. To assess the Pseudomonas aeruginosa susceptibility to C/T, a surveillance study was conducted from October 2018 to March 2019 at the University Hospital "Ospedali Riuniti" of Ancona (Italy).

MATERIALS AND METHODS

MICs to C/T were determined by Etest strip. Resistant isolates were characterized by phenotypic (broth microdilution antimicrobial susceptibility testing and mCIM) and genotypic (PCR, PFGE and WGS) methods. Clinical variables of patients infected by C/T resistant P. aeruginosa were collected from medical records.

RESULTS

fifteen out of 317 P. aeruginosa collected showed resistance to C/T (4.7%). Ten strains demonstrated a carbapenemase activity by mCIM method, and PCR confirmed eight of them harbored a bla_VIM gene, while the other two were positive for bla_IMP. Additionally, three isolates carried acquired extended spectrum β-lactamase genes (2 bla_PER and 1 bla_GES). Eight strains were strictly related by PFGE and WGS analysis confirmed that they belonged to ST111. The other STs found were ST175 (2 isolates), ST235 (2 isolates), ST70 (1 isolate), ST621 (1 isolate) and the new ST3354 (1 isolate). Most of the patients received previous antibiotic therapies, carried invasive devices and had a prolonged hospitalization.

CONCLUSION

This study demonstrated the presence of C/T resistant P. aeruginosa isolates also in a regional hospital, carrying a number of resistance mechanisms acquired by different high-risk clones.

Genomic Characterization of Mutli-Drug Resistant Pseudomonas aeruginosa Clinical Isolates: Evaluation and Determination of Ceftolozane/Tazobactam Activity and Resistance Mechanisms

Resistance to ceftolozane/tazobactam (C/T) in Pseudomonas aeruginosa is a health concern. In this study, we conducted a whole-genome-based molecular characterization to correlate resistance patterns and β-lactamases with C/T resistance among multi-drug resistant P. aeruginosa clinical isolates. Resistance profiles for 25 P. aeruginosa clinical isolates were examined using disk diffusion assay. Minimal inhibitory concentrations (MIC) for C/T were determined by broth microdilution. Whole-genome sequencing was used to check for antimicrobial resistance determinants and reveal their genetic context. The clonal relatedness was evaluated using MLST, PFGE, and serotyping. All the isolates were resistant to C/T. At least two β-lactamases were detected in each with the bla_OXA-4, bla_OXA-10, bla_OXA-50, and bla_OXA-395 being the most common. bla_IMP-15, bla_NDM-1, or bla_VIM-2, metallo-β-lactamases, were associated with C/T MIC >256 μg/mL. Eight AmpC variants were identified, and PDC-3 was the most common. We also determined the clonal relatedness of the isolates and showed that they grouped into 11 sequence types (STs) some corresponding to widespread clonal complexes (ST111, ST233, and ST357). C/T resistance was likely driven by the acquired OXA β-lactamases such as OXA-10, and OXA-50, ESBLs GES-1, GES-15, and VEB-1, and metallo- β-lactamases IMP-15, NDM-1, and VIM-2. Collectively, our results revealed C/T resistance determinants and patterns in multi-drug resistant P. aeruginosa clinical isolates. Surveillance programs should be implemented and maintained to better track and define resistance mechanisms and how they accumulate and interact.

Recent Developments to Cope the Antibacterial Resistance via β-Lactamase Inhibition

Antibacterial resistance towards the β-lactam (BL) drugs is now ubiquitous, and there is a major global health concern associated with the emergence of new β-lactamases (BLAs) as the primary cause of resistance. In addition to the development of new antibacterial drugs, β-lactamase inhibition is an alternative modality that can be implemented to tackle this resistance channel. This strategy has successfully revitalized the efficacy of a number of otherwise obsolete BLs since the discovery of the first β-lactamase inhibitor (BLI), clavulanic acid. Over the years, β-lactamase inhibition research has grown, leading to the introduction of new synthetic inhibitors, and a few are currently in clinical trials. Of note, the 1, 6-diazabicyclo [3,2,1]octan-7-one (DBO) scaffold gained the attention of researchers around the world, which finally culminated in the approval of two BLIs, avibactam and relebactam, which can successfully inhibit Ambler class A, C, and D β-lactamases. Boronic acids have shown promise in coping with Ambler class B β-lactamases in recent research, in addition to classes A, C, and D with the clinical use of vaborbactam. This review focuses on the further developments in the synthetic strategies using DBO as well as boronic acid derivatives. In addition, various other potential serine- and metallo- β-lactamases inhibitors that have been developed in last few years are discussed briefly as well. Furthermore, binding interactions of the representative inhibitors have been discussed based on the crystal structure data of inhibitor-enzyme complex, published in the literature.

The primary pharmacology of ceftazidime/avibactam: in vitro translational biology

Previous reviews of ceftazidime/avibactam have focused on in vitro molecular enzymology and microbiology or the clinically associated properties of the combination. Here we take a different approach. We initiate a series of linked reviews that analyse research on the combination that built the primary pharmacology data required to support the clinical and business risk decisions to perform randomized controlled Phase 3 clinical trials, and the additional microbiological research that was added to the above, and the safety and chemical manufacturing and controls data, that constituted successful regulatory licensing applications for ceftazidime/avibactam in multiple countries, including the USA and the EU. The aim of the series is to provide both a source of reference for clinicians and microbiologists to be able to use ceftazidime/avibactam to its best advantage for patients, but also a case study of bringing a novel β-lactamase inhibitor (in combination with an established β-lactam) through the microbiological aspects of clinical development and regulatory applications, updated finally with a review of resistance occurring in patients under treatment. This first article reviews the biochemistry, structural biology and basic microbiology of the combination, showing that avibactam inhibits the great majority of serine-dependent β-lactamases in Enterobacterales and Pseudomonas aeruginosa to restore the in vitro antibacterial activity of ceftazidime. Translation to efficacy against infections in vivo is reviewed in the second co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac172).

Combination of phage therapy and cefiderocol to successfully treat Pseudomonas aeruginosa cranial osteomyelitis

Background

Pseudomonas aeruginosa has the ability to exhibit resistance to a broad range of antibiotics, highlighting the importance of identifying alternative or adjunctive treatment options, such as phages.

Patients and methods

We report the case of a 25-year-old male who experienced an accidental electrocution resulting in exposed calvarium in the left parieto-temporal region, complicated by a difficult-to-treat P. aeruginosa (DTR-P. aeruginosa) infection. Cefiderocol was the sole antibiotic with consistent activity against six bacterial isolates obtained from the infected region over a 38 day period.

Results

WGS analysis identified a bla GES-1 gene as well as the MDR efflux pumps MexD and MexX in all six of the patient's ST235 DTR-P. aeruginosa isolates, when compared with the reference genome P. aeruginosa PA01 and a P. aeruginosa ST235 isolate from an unrelated patient. After debridement of infected scalp and bone, the patient received approximately 6 weeks of cefiderocol in conjunction with IV phage Pa14NPøPASA16. Some improvement was observed after the initiation of cefiderocol; however, sustained local site improvement and haemodynamic stability were not achieved until phage was administered. No medication-related toxicities were observed. The patient remains infection free more than 12 months after completion of therapy.

Conclusions

This report adds to the growing literature that phage therapy may be a safe and effective approach to augment antibiotic therapy for patients infected with drug-resistant pathogens. Furthermore, it highlights the importance of the GES β-lactamase family in contributing to inactivation of a broad range of β-lactam antibiotics in P. aeruginosa, including ceftolozane/tazobactam, ceftazidime/avibactam and imipenem/relebactam.

Synergistic Activity of Imipenem in Combination with Ceftazidime/Avibactam or Avibactam against Non-MBL-Producing Extensively Drug-Resistant Pseudomonas aeruginosa

Extensively drug-resistant Pseudomonas aeruginosa (XDRPA) infection is a significant public health threat due to a lack of effective therapeutic options. New β-lactam-β-lactamase inhibitor combinations, including ceftazidime-avibactam (CZA), have shown a high resistance rate to XDRPA. This study was therefore conducted to describe the underlying genomic mechanism of resistance for CZA nonsusceptible XDRPA strains that are non-metallo-β-lactamase (MBL) producers as well as to examine synergism of CZA and other antipseudomonal agents. Furthermore, the synergistic antibacterial activity of the most effective antimicrobial combination against non-MBL-producing XDRPA was evaluated through in vitro experiments. The resistance profiles of 15 CZA-resistant XDRPA strains isolated from clinical specimens in China-Japan Friendship Hospital between January 2017 to December 2020 were obtained by whole-genome sequencing (WGS) analysis. MBL genes bla_IMP-1 and bla_IMP-45 were found in 2 isolates (2/15, 13.3%); the other underlying CZA-resistance mechanisms involved the decreased OprD porin (13/13), bla_AmpC overexpression (8/13) or mutation (13/13), and upregulated efflux pumps (13/13). CZA-imipenem (CZA-IPM) combination was identified to be the most effective against non-MBL-producing XDRPA according to the results of WGS analysis and combined antimicrobial susceptibility tests, with an approximately 16.62-fold reduction in MICs compared to CZA alone. Furthermore, the results of checkerboard analysis and growth curve displayed the synergistic antimicrobial activity of CZA and IPM against non-MBL-producing XDRPA. Electron microscopy also revealed that CZA-IPM combination might lead to more cellular structural alterations than CZA or IPM alone. This study suggested that the CZA-IPM combination has potential for non-MBL-producing XDRPA with bla_AmpC overexpression or mutation, decreased OprD porin, and upregulated efflux pumps. IMPORTANCE Handling the infections by extensively drug-resistant Pseudomonas aeruginosa (XDRPA) strains is challenging due to their complicated antibiotic resistance mechanisms in immunosuppressed patients with pulmonary diseases (e.g., cystic fibrosis, chronic obstructive pulmonary disease, and lung transplant), ventilator-associated pneumonia, and bloodstream infections. The current study suggested the potentiality of the ceftazidime-avibactam-imipenem combination against XDRPA with bla_AmpC overexpression or mutation, decreased OprD porin, and/or upregulated efflux pumps. Our findings indicate the necessity of combined drug sensitivity tests against XDRPA and also lay a foundation for the development of prevention, control, and treatment strategies in XDRPA infections.

High prevalence of blaVEB , blaGES and blaPER genes in beta-lactam resistant clinical isolates of Pseudomonas aeruginosa

The increased prevalence of β-lactamase is one of the main factors in resistance to β-lactams in Pseudomonas aeruginosa. This study aimed to investigate the prevalence of blaVEB , blaPER , and blaGES genes in β-lactam-resistant P. aeruginosa. We collected 100 non-duplicated clinical isolates of P. aeruginosa and identified them by standard tests. Using disk agar diffusion test, we detected the β-lactam-resistant isolates and extracted the DNAs of the isolates by alkaline lysis method. Then, the prevalence of blaVEB , blaPER and blaGES genes were detected by PCR method. The results were assessed by SPSS 21 software and Chi-square test. Out of 100 isolates, 43% were detected as resistant against at least one of the beta-lactams tested. Piperacillin-tazobactam was the most effective antibiotic, while 39% and 37% of the isolates were resistant to aztreonam and meropenem, respectively. A significant relationship was observed between the resistance to tested antibiotics and the presence of blaVEB , blaGES , and blaPER genes. Among 43 isolates that were resistant to at least one of the tested β-lactams, 93.02%, 83.72%, and 81.39% of them carried blaVEB , blaGES , and blaPER genes, respectively. According to this study and due to high prevalence of β-lactam resistance genes, it is better to check the level of antibiotic resistance and resistance genes for better management of patients with infection caused by this bacterium. Also, high prevalence of class A β-lactamases indicates the significant role of these enzymes in emerging resistance to beta-lactams.

Impact of Acquired Broad-Spectrum β-Lactamases on Susceptibility to Cefiderocol and Newly Developed β-Lactam/β-Lactamase Inhibitor Combinations in Escherichia coli and Pseudomonas aeruginosa

The ability of broad-spectrum β-lactamases to reduce the susceptibility to ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam (AZA), and cefiderocol (FDC) was evaluated both in Pseudomonas aeruginosa and in Escherichia coli using isogenic backgrounds. Although metallo-β-lactamases conferred resistance in most cases, except for AZA, several clavulanic-acid-inhibited extended-spectrum β-lactamases (PER, BEL, SHV) had a significant impact on the susceptibility to CZA, C/T, and FDC.

Aliidiomarina shirensis as Possible Source of the Integron- and Plasmid-Mediated Fosfomycin Resistance Gene fosC2

In-silico analysis and cloning experiments identified a fosC2-like fosfomycin resistance gene in the chromosome of Aliidiomarina shirensis, with our data suggesting that this bacterium might be added to the list of species identified as reservoirs of fos-like genes that were subsequently acquired by other Gram-negative species. Indeed, the fosC2 gene was identified as acquired in Providencia huaxinensis and Aeromonas hydrophila isolates, with this gene being located in class 1 integron structures in the latter cases. Biochemical characterization and site-directed mutagenesis showed a higher catalytic efficiency for the intrinsic FosC2^AS (from A. shirensis) than for the acquired FosC2 (from P. huaxinensis) enzyme due to a single substitution in the amino acid sequence (Gly43Glu). Notably, this study constitutes the first identification of the likely natural reservoir of a complete gene cassette (including its attC site).

Therapeutic Strategies for Emerging Multidrug-Resistant Pseudomonas aeruginosa

Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates are frequent causes of serious nosocomial infections that may compromise the selection of antimicrobial therapy. The goal of this review is to summarize recent epidemiologic, microbiologic, and clinical data pertinent to the therapeutic management of patients with infections caused by MDR/XDR-P. aeruginosa. Historically, conventional antipseudomonal β-lactam antibiotics have been used for the empiric treatment of MDR/XDR-P. aeruginosa. Owing to the remarkable capacity of P. aeruginosa to confer resistance via multiple mechanisms, these traditional therapies are often rendered ineffective. To increase the likelihood of administering empiric antipseudomonal therapy with in vitro activity, a second agent from a different antibiotic class is often administered concomitantly with a traditional antipseudomonal β-lactam. However, combination therapy may pose an increased risk of antibiotic toxicity and secondary infection, notably, Clostridioides difficile. Multiple novel agents that demonstrate in vitro activity against MDR-P. aeruginosa (e.g., β-lactam/β-lactamase inhibitor combinations and cefiderocol) have been recently granted US Food and Drug Administration (FDA) approval and are promising additions to the antipseudomonal armamentarium. Even so, comparative clinical data pertaining to these novel agents is sparse, and concerns surrounding the scarcity of antibiotics active against refractory MDR/XDR-P. aeruginosa necessitates continued assessment of alternative therapies. This is particularly important in patients with cystic fibrosis (CF) who may be chronically colonized and suffer from recurrent infections and disease exacerbations due in part to limited efficacious antipseudomonal agents. Bacteriophages represent a promising candidate for combatting recurrent and refractory infections with their ability to target specific host bacteria and circumvent traditional mechanisms of antibiotic resistance seen in MDR/XDR-P. aeruginosa. Future goals for the management of these infections include increased comparator clinical data of novel agents to determine in what scenario certain agents may be preferred over others. Until then, appropriate treatment of these infections requires a thorough evaluation of patient- and infection-specific factors to guide empiric and definitive therapeutic decisions.

Association of blaVIM-2, blaPDC-35, blaOXA-10, blaOXA-488 and blaVEB-9 β-Lactamase Genes with Resistance to Ceftazidime–Avibactam and Ceftolozane–Tazobactam in Multidrug-Resistant Pseudomonas aeruginosa

Ceftazidime–avibactam and ceftolozane–tazobactam are approved for the treatment of complicated Gram-negative bacterial infections including multidrug-resistant (MDR) Pseudomonas aeruginosa. Resistance to both agents has been reported, but the underlying mechanisms have not been fully explored. This study aimed to correlate β-lactamases with phenotypic resistance to ceftazidime–avibactam and/or ceftolozane–tazobactam in MDR-P. aeruginosa from Qatar. A total of 525 MDR-P. aeruginosa isolates were collected from clinical specimens between 2014 and 2017. Identification and antimicrobial susceptibility were performed by the BD Phoenix^TM system and gradient MIC test strips. Of the 75 sequenced MDR isolates, 35 (47%) were considered as having difficult-to-treat resistance, and 42 were resistant to ceftazidime–avibactam (37, 49.3%), and/or ceftolozane–tazobactam (40, 53.3%). They belonged to 12 sequence types, with ST235 being predominant (38%). Most isolates (97.6%) carried one or more β-lactamase genes, with bla_OXA-488 (19%) and bla_VEB-9 (45.2%) being predominant. A strong association was detected between class B β-lactamase genes and both ceftazidime–avibactam and ceftolozane–tazobactam resistance, while class A genes were associated with ceftolozane–tazobactam resistance. Co-resistance to ceftazidime–avibactam and ceftolozane–tazobactam correlated with the presence of bla_VEB-9, bla_PDC-35, bla_VIM-2, bla_OXA-10 and bla_OXA-488. MDR-P. aeruginosa isolates resistant to both combination drugs were associated with class B β-lactamases (bla_VIM-2) and class D β-lactamases (bla_OXA-10), while ceftolozane–tazobactam resistance was associated with class A (bla_VEB-9), class C (bla_VPDC-35), and class D β-lactamases (bla_OXA-488).

First Report of bla OXA-677 with Enhanced Meropenem-Hydrolyzing Ability in Pseudomonas aeruginosa in China

Purpose

OXA-10-type class D β-lactamases have shown their evolutionary potential of enhancing carbapenem resistance. This study aimed to elucidate the role of OXA-10 variants in clinical isolated multidrug resistant (MDR) Pseudomonas aeruginosa and characterize the first appearance of OXA-677 in China.

Methods

Six bla_OXA-10-like-positive strains were screened by PCR from 41 P. aeruginosa strains, which were resistant to both carbapenems and ceftazidime-avibactam, collected across China in 2018. The minimum inhibitory concentrations (MIC) were determined with the broth microdilution method. The resistance-associated genes and genetic environment were investigated by whole-genome sequencing (WGS). The function and mechanism of OXA-677 β-lactamase were identified by molecular cloning and protein structure modeling.

Results

All the bla_OXA-10-like-positive Pseudomonas aeruginosa were MDR strains. They also had outer membrane porin defects and produced β-lactam resistance gene bla_PER-1, fluoroquinolone-resistant gene crpP, aminoglycoside-resistance gene aph(3ʹ)-IIb, aph(6)-Id, aacA and aadA, fosfomycin-resistance gene fosA, sulfamethoxazole-resistance gene sul1, and chloramphenicol-resistance gene catB7. All bla_OXA-10 variants were located in a Tn1403-related transposon, containing aacA4-12-bla_OXA-677-aadA1, aacA4-12-bla_OXA-101-aadA5, and bla_OXA-246-aacA3-aadA13 gene cassette arrays, respectively. Notably, the bla_OXA-677 producer showed a high MIC level of meropenem (MIC>64 mg/L). Compared to bla_OXA-10, bla_OXA-677 was found a G-to-T transversion at position 350, leading to a phenylalanine-for-valine substitution in position 117, which is closer to leucine155 in the omega loop of the active site. MIC of meropenem for E. coli DH5α with the recombinant plasmid pHSG398 carrying bla_OXA-677 was elevated by 8 times.

Conclusion

We speculate that the OXA-10-like enzymes and the decrease of membrane permeability confer carbapenem resistance, and the V117 substitution in OXA-677 might lead to a higher resistance level of meropenem.

Selection of AmpC β-lactamase variants and metallo-β-lactamases leading to ceftolozane/tazobactam and ceftazidime/avibactam-resistance during treatment of MDR/XDR Pseudomonas aeruginosa infections

Infections caused by ceftolozane/tazobactam and ceftazidime/avibactam-resistant P. aeruginosa infections are an emerging concern. We aimed to analyze the underlying ceftolozane/tazobactam and ceftazidime/avibactam resistance mechanisms in all MDR/XDR P. aeruginosa isolates recovered during one year (2020) from patients with a documented P. aeruginosa infection. Fifteen isolates showing ceftolozane/tazobactam and ceftazidime/avibactam resistance were evaluated. Clinical conditions, previous positive cultures and β-lactams received in the previous month were reviewed for each patient. MICs were determined by broth microdilution. MLSTs and resistance mechanisms were determined using short- and long-read WGS. The impact of PDCs on β-lactam resistance was demonstrated by cloning into an ampC-deficient PAO1 derivative (PAOΔC) and construction of 3D models. Genetic support of acquired β-lactamases was determined in silico from high-quality hybrid assemblies. In most cases, the isolates were recovered after treatment with ceftolozane/tazobactam or ceftazidime/avibactam. Seven isolates from different STs owed their β-lactam resistance to chromosomal mutations and all displayed specific substitutions in PDC: Phe121Leu and Gly222Ser, Pro154Leu, Ala201Thr, Gly214Arg, ΔGly203-Glu219 and Glu219Lys. In the other eight isolates, the ST175 clone was overrepresented (6 isolates) and associated with IMP-28 and IMP-13, whereas two ST1284 isolates produced VIM-2. The cloned PDCs conferred enhanced cephalosporin resistance. 3D PDC models revealed rearrangements affecting residues involved in cephalosporin hydrolysis. Carbapenemases were chromosomal (VIM-2) or plasmid-borne (IMP-28, IMP-13), and associated with class-1 integrons located in Tn402-like transposition modules. Our findings highlight that cephalosporin/ß-lactamase inhibitors are potential selectors of MDR/XDR P. aeruginosa strains producing PDC variants or metallo-ß-lactamases. Judicious use of these agents is encouraged.