30th April 2024

This month’s Editors’ picks in the Journal of Antimicrobial Chemotherapy (JAC) and JAC-Antimicrobial Resistance (JAC-AMR): are we overlooking some carbapenemase-producing Enterobacterales? Plus, the mechanism matters – MIC alone cannot predict temocillin susceptibility; why we need a standard definition for healthcare-associated pneumonia; and more.

Mathilde Duque and others, Comparison of the French novel disc diffusion-based algorithm and the current EUCAST guidelines for the screening of carbapenemase-producing Enterobacterales. Journal of Antimicrobial Chemotherapy, dkae054, https://doi.org/10.1093/jac/dkae054

In this research letter, Duque et al. report that the current EUCAST meropenem disc diffusion screening cut-off cannot be relied on to detect OXA-48-like producers, with more than 40% falsely identified as non-carbapenemase-producing Enterobacterales. Performance was particularly poor for OXA-244 producers, which are becoming increasingly prevalent in Europe—of concern as this could lead to underreporting. Updating detection methods is crucial to stay ahead of evolving antibiotic resistance.

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Elise Mallart and others, Impact of the phenotypic expression of temocillin resistance in Escherichia coli on temocillin efficacy in a murine peritonitis model. Journal of Antimicrobial Chemotherapy, dkae072, https://doi.org/10.1093/jac/dkae072

Mallart et al. examined different temocillin resistance mechanisms in E. coli and found that even with high MICs, unfavourable pharmacokinetics/pharmacodynamics and no fitness cost, heteroresistant strains with NmpC porin alteration and efflux pump modification were still susceptible to temocillin. However, when the resistance mechanism was homogeneously expressed BaeS efflux pump alteration and the MIC was similar, temocillin was ineffective. MIC alone may not be enough to predict temocillin’s success.

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Luke S P Moore and others, Antimicrobial stewardship markers and healthcare-associated pneumonia threshold criteria in UK hospitals: analysis of the MicroGuide™ application. JAC-Antimicrobial Resistance 2024, dlae058, https://doi.org/10.1093/jacamr/dlae058

In the UK, many hospitals host their local antimicrobial guidelines on the MicroGuide™ digital app. Moore et al. examined MicroGuide™ content relating to healthcare-associated pneumonia (HAP) and found inconsistency in how hospitals define HAP. They recommend creating a standard definition for HAP, to help reduce subjectivity in diagnosis and optimize management and stewardship.

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Jule Rutz and others, Individual and institutional predisposing factors of MRSA surgical site infection and outcomes—a retrospective case-control-study in 14 European high-volume surgical centres. JAC-Antimicrobial Resistance 2024, dlae046, https://doi.org/10.1093/jacamr/dlae046

In this study of surgical site infections (SSI) caused by MRSA in Europe, Rutz et al. found a low overall MRSA SSI rate (0.06%) but there were significant differences between countries and hospitals. Hospitals with established antibiotic stewardship and infectious disease programmes had lower MRSA rates, but only 3 of the 14 participating centres had such programmes. MRSA SSI patients were older and had more comorbidities than those with MSSA SSI.

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Anja Berger and others, Corynebacterium diphtheriae and Corynebacterium ulcerans: development of EUCAST methods and generation of data on which to determine breakpoints. Journal of Antimicrobial Chemotherapy, dkae056, https://doi.org/10.1093/jac/dkae056

Berger et al. used broth microdilution and disc diffusion methods to develop a dataset of MIC values and inhibition zone diameters for Corynebacterium diphtheriae and Corynebacterium ulcerans. They included 400 isolates from two European reference laboratories representing a range of susceptibilities for each antimicrobial class. The resulting dataset enabled EUCAST to define breakpoints for diphtheria.

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Christina K Lin and others, Rates of resistance and heteroresistance to newer β-lactam/β-lactamase inhibitors for carbapenem-resistant Enterobacterales. JAC-Antimicrobial Resistance 2024, dlae048, https://doi.org/10.1093/jacamr/dlae048

Lin et al. found that a significant proportion (24%) of carbapenem-resistant Enterobacterales (CRE) were either resistant or had subpopulations resistant (heteroresistant) to at least one newer β-lactam/β-lactamase inhibitor combination. While these antibiotics are still effective for most CRE, this trend highlights the need for better antibiotic use and understanding of the local antibiogram.

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