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

Geographic variations in distributions of carbapenemase-encoding genes, susceptibilities, and minimum inhibitory concentrations of inpatient meropenem-resistant Enterobacterales to ceftazidime-avibactam, meropenem-vaborbactam, and aztreonam-avibactam across four global regions: 2020-2022 data from the Antimicrobial Testing Leadership and Surveillance

PURPOSE

To evaluate the susceptibility profiles of regional inpatient meropenem-resistant (MEM-R) carbapenemase-producing Enterobacterales (CPE) isolates and their MIC values to ceftazidime-avibactam (CZA), meropenem-vaborbactam (MVB), and aztreonam-avibactam (ATM-AVI) METHODS: The 2020-2022 Antimicrobial Testing Leadership and Surveillance database were analyzed. Carbapenemase-encoding genes in CPE isolates were identified using multiplex PCR and Sanger sequencing. Susceptibility breakpoints for CZA and MVB recommended by CLSI 2024 and EUCAST 2025 against Enterobacterales were applied.

RESULTS

A total of 2,318 CPE isolates (78.2% were Klebsiella pneumoniae) were tested globally. Notable diversity in carbapenemase-encoding gene distributions was observed among CPE isolates from Africa/the Middle East (10 countries; n=361), Asia (7 countries, excluding India and Pakistan; n=182), Europe (17 countries; n=1,002), and Latin America (10 countries; n=773). Metallo-β-lactamase-encoding genes, predominantly blaNDM-1, were more frequently detected in CPE isolates from Africa/the Middle East (75.3%, except blaNDM-5 in Kuwait) and Asia (67%, except blaIMP-8 in Taiwan) compared to other regions. Among KPC variants, the KPC-2 enzyme was the predominant one in CPE isolates in Europe (43.4%, except for KPC-3 prevalent specifically in Italy) and in Latin America (62.1%). The susceptibility rates of all analyzed CPE isolates harboring only a single blaKPC gene to CZA and MVB were 99.4% and 93.5%, respectively, based on the CLSI 2024 susceptibility breakpoints. The MIC50/90 values of CPE isolates to ATM-AVI were 0.12/0.25 mg/L and 0.5/1 mg/L, respectively, regardless of collection region, dual carbapenemase production, or infection source.

CONCLUSIONS

The trends in resistance to novel antibiotics among contemporary CPE isolates need close monitoring.

Successful treatment of an intra-abdominal abscess caused by KPC-2-producing hypervirulent Klebsiella pneumoniae sequence type 11 with imipenem/cilastatin/relebactam in a Japanese patient

KPC-producing K. pneumoniae is rare in Japan. In China, KPC-2-producing sequence type (ST)11 K. pneumoniae isolates have been rapidly increasing, and a subset of these isolates have acquired hypervirulence. We report a case of a 39-year-old Japanese male who developed bacteremia and intra-abdominal abscesses caused by hypervirulent carbapenem-resistant K. pneumoniae. The patient sustained abdominal injuries following a traffic accident in Xinjiang Uygur Autonomous Region and underwent abdominal surgery before being transferred to our hospital. Abscess drainage was performed, and he was initially treated with meropenem (2 g every 8 hours, prolonged infusion over 3 hours), gentamicin (5 mg/kg/day), and tigecycline (200 mg as a loading, followed by 100 mg every 12 hours). KPC carbapenemase was detected using the NG-Test® CARBA 5 (NG Biotech, France), and the minimum inhibitory concentration for imipenem/cilastatin/relebactam was 1 μg/mL, indicating susceptibility. His treatment was switched to imipenem/cilastatin/relebactam (1 g every 6 hours) for 7 weeks, resulting in clinical improvement. Whole-genome sequencing analysis revealed that the causative strain was hypervirulent KPC-2-producing K. pneumoniae (capsular type K64, ST 11) carrying blaKPC-2 and blaCTX-M-65 on a multireplicon plasmid (pMTY24772_IncFII-R), which was a fusion of IncFII and IncR. Additionally, rmpA and iucABCD genes associated with hypervirulence were detected. The strain carried a resistance plasmid and a virulence plasmid similar to those carried by ST11-K64 KPC-producing strains reported from China. Imipenem/cilastatin/relebactam is potentially an option for treating infections caused by KPC-2-producing hypervirulent K, pneumoniae with porin mutations. Cross-border spread of pathogens that are both multidrug-resistant and hyperviirulent must be closely monitored.

Activity of imipenem/relebactam against KPC-producing Klebsiella pneumoniae and the possible role of Ompk36 mutation in determining resistance: an Italian retrospective analysis

BACKGROUND

Antimicrobial resistance in Enterobacterales represents a substantial threat in modern clinical practice and the collection of data on the efficacy of new molecules is of paramount importance. Our study aimed to analyse the in vitro activity of imipenem/cilastatin/relebactam (IMI/REL) against KPC-producing Klebsiella pneumoniae (KPC-Kp) and investigate the genetic determinants of resistance to this agent.

METHODS

A total of 603 KPC-Kp strains, which were randomly collected during a multicentre study in northern Italy in the period 2016-2018, were analysed retrospectively. Antibiotic susceptibility testing was performed using a commercial broth microdilution. IMI-REL-resistant KPC-Kp strains were further analysed by whole genome sequencing to identify resistance determinants.

RESULTS

Ninety-eight percent of KPC-Kp (591/603) showed in vitro susceptibility to IMI/REL, with a minimum inhibitory concentration below the EUCAST cut-off. Different mutations in OmpK36 were found in all 12 IMI/REL-resistant strains, which belonged to MLST STs 258 (3 isolates), 307 (8 isolates) and 512 (1 isolate), but no clonal relatedness was detected by the minimum spanning tree analysis, except for 2 strains isolated in the same hospital. Equal distribution of blaKPC-2 (6/12) and blaKPC-3 (6/12) was found, and in 11 isolates the presence of genetic variants associated with the production of beta-lactamases was also identified. KPC-Kp resistant to IMI/REL retained susceptibility to meropenem/vaborbactam (MVB, 12/12, 100%) and ceftazidime/avibactam (CZA, 11/12, 91.7%). Only one strain of 603 was resistant to either MVB and CZA but susceptible to IMI/REL with a MIC of 2 mg/L; 4/603 (0.7%) were resistant to CZA but susceptible to IMI/REL and MVB.

CONCLUSIONS

IMI/REL showed good in vitro activity against the KPC-Kp strains analysed. All the IMI/REL-resistant strains displayed a mutation in porin OmpK36 and produced carbapenemases, with KPC-2 and KPC-3 being equally distributed. MVB and CZA maintained good activity against IMI/REL resistant isolates.

Emergence of high-level aztreonam-avibactam and cefiderocol resistance following treatment of an NDM-producing Escherichia coli bloodstream isolate exhibiting reduced susceptibility to both agents at baseline

Background

Cefiderocol (FDC) or ceftazidime-avibactam with aztreonam (CZA-ATM) are frontline agents for New Delhi metallo-β-lactamase (NDM)-producing Enterobacterales; however, clinical data are scarce, and mechanisms of treatment-emergent resistance are ill-defined. Our objectives were to characterize serial isolates and stool microbiota from a liver transplant recipient with NDM-producing Escherichia coli bacteraemia.

Methods

Isolates collected pre- and post-CZA-ATM treatment underwent broth microdilution susceptibility testing and whole-genome sequencing. Longitudinal stool collected during CZA-ATM therapy underwent metagenomic sequencing (Nanopore MinION).

Results

The baseline isolate exhibited elevated MICs for ATM-AVI (16/4 µg/mL) and FDC (8 µg/mL). Posttreatment, a rectal surveillance isolate exhibited high-level resistance to ATM-AVI (> 128/4 µg/mL) and FDC (32 µg/mL). Both isolates belonged to ST361 and harboured WT bla NDM-5. The baseline isolate contained wild type (WT) bla CMY-145 and mutations in ftsI (which encodes PBP3), including a YRIN insertion at residue 338 and the non-synonymous substitutions Q227H, E353K and I536L. The posttreatment isolate harboured new mutations in ftsI (A417 V) and bla CMY-145 (L139R and N366Y). Analysis of four stool samples collected during CZA-ATM treatment revealed high E. coli abundance. E. coli relative abundance increased from 34.5% (first sample) to 61.9% (last sample).

Conclusions

Baseline mutations in ftsI were associated with reduced susceptibility to ATM-AVI and FDC in an ST361 NDM-5-producing E. coli bloodstream isolate. High-level resistance was selected after CZA-ATM treatment, resulting in new ftsl and bla CMY-145 mutations. These findings underscore the need for ATM-AVI susceptibility testing for NDM producers, and the potential for PBP3 mutations to confer cross-resistance to ATM-AVI and FDC, which can emerge after CZA-ATM treatment.

In vitro activity of meropenem-vaborbactam plus aztreonam against metallo-β-lactamase-producing Klebsiella pneumoniae

We evaluated the in vitro activity of meropenem-vaborbactam plus aztreonam (MEV-ATM) against 140 metallo-β-lactamase (MBL)-producing Klebsiella pneumoniae isolates. Among them, 25 isolates (17.9%) displayed minimum inhibitory concentrations (MIC) ≥ 8 µg/mL, while 112 (80.0%) had MIC ≤ 2 µg/mL. Genomic analysis and subsequent gene cloning experiments revealed OmpK36 134-135GD-insertion and increased carbapenemase gene (blaNDM-1 and blaOXA-48-like) copy numbers are the main factors responsible for MEV-ATM non-susceptibility. Notably, MEV-ATM is actively against aztreonam-avibactam-resistant mutants due to CMY-16 mutations.

Ceftazidime/Avibactam and Meropenem/Vaborbactam for the Management of Enterobacterales Infections: A Narrative Review, Clinical Considerations, and Expert Opinion

This comprehensive review examines the unique attributes, distinctions, and clinical implications of ceftazidime-avibactam (CAZ-AVI) and meropenem-vaborbactam (MEM-VAB) against difficult-to-treat Enterobacterales infections. Our manuscript explores these antibiotics' pharmacokinetic and pharmacodynamic properties, antimicrobial activities, in vitro susceptibility testing, and clinical data. Moreover, it includes a meticulous examination of comparative clinical and microbiological studies, assessed and presented to provide clarity in making informed treatment choices for clinicians. Finally, we propose an expert opinion from a microbiological and a clinical point of view about their use in appropriate clinical settings. This is the first review aiming to provide healthcare professionals with valuable insights for making informed treatment decisions when combating carbapenem-resistant pathogens.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

A Whole-Genome Sequencing-Based Approach for the Characterization of Klebsiella pneumoniae Co-Producing KPC and OXA-48-like Carbapenemases Circulating in Sardinia, Italy

BACKGROUND

Whole-genome sequencing (WGS) provides important information for the characterization, surveillance, and monitoring of antimicrobial resistance (AMR) determinants, particularly in cases of multi- and extensively drug-resistant microorganisms. We reported the results of a WGS analysis carried out on carbapenemases-producing Klebsiella pneumoniae, which causes hospital-acquired infections (HAIs) and is characterized by a marked resistance profile.

METHODS

Clinical, phenotypic, and genotypic data were collected for the AMR surveillance screening program of the University Hospital of Sassari (Italy) during 2020-2021. Genomic DNA was sequenced using the Illumina Nova Seq 6000 platform. Final assemblies were manually curated and carefully verified for the detection of antimicrobial resistance genes, porin mutations, and virulence factors. A phylogenetic analysis was performed using the maximum likelihood method.

RESULTS

All 17 strains analyzed belonged to ST512, and most of them carried the blaKPC-31 variant blaOXA-48-like, an OmpK35 truncation, and an OmpK36 mutation. Phenotypic analysis showed a marked resistance profile to all antibiotic classes, including β-lactams, carbapenems, aminoglycosides, fluoroquinolone, sulphonamides, and novel β-lactam/β-lactamase inhibitors (BL/BLI).

CONCLUSION

WGS characterization revealed the presence of several antibiotic resistance determinants and porin mutations in highly resistant K. pneumoniae strains responsible for HAIs. The detection of blaKPC-31 in our hospital wards highlights the importance of genomic surveillance in hospital settings to monitor the emergence of new clones and the need to improve control and preventive strategies to efficiently contrast AMR.