Comparison of carbapenem minimum inhibitory concentrations of OXA-48-like Klebsiella pneumoniae by Sensititre, Vitek 2, MicroScan and Etest

New Option for Antibiotic Susceptibility Testing in Clinical Practice: Performance Evaluation of AutoMic-i600 Automatic System Based on Broth Microdilution Method

Background

The emergence of multidrug-resistant bacteria limits antibiotic efficacy, making accurate antimicrobial susceptibility testing (AST) essential for clinical decisions. Broth microdilution (BMD) is the gold standard but is impractical for routine application. Current automated AST systems improve efficiency but face accuracy or operational challenges, highlighting the need for reliable and user-friendly solutions.

Objective

This study aims to evaluate the performance of a novel automated AST system (AutoMic-i600) based on the BMD method for AST of common clinical bacteria.

Methods

A total of 229 clinical isolates (150 Gram-negative and 79 Gram-positive) were prospectively collected from microbiology laboratory between June 2023 and August 2023. We reported the comparison of the AutoMic-i600 and Vitek 2 systems for routine antibiotics, and also validated the detection performance of AutoMic-i600 for novel antibiotics, based on the BMD method.

Results

The overall essential agreement (EA) and categorical agreement (CA) between AutoMic-i600 and BMD were 93.2% and 93.5% for Gram-negative bacteria and 98.5% and 97.8% for Gram-positive bacteria, respectively. The overall EA and CA between Vitek 2 and BMD were 92.6% and 93.5% for Gram-negative bacteria and 97.9% and 97.4% for Gram-positive bacteria. Importantly, for drug-resistant bacteria, AutoMic-i600 demonstrated a higher overall agreement than Vitek 2 (EA: 98.1% vs 94.8%, CA: 97.5% vs 92.0%), especially in Gram-negative bacteria (EA: 97.7% vs 93.5%, CA: 97.7% vs 89.3%). The VME rate for Gram-negative bacteria using AutoMic-i600 was significantly lower than that of Vitek 2 (1.0% vs 2.9%). Novel antibiotics detected by AutoMic-i600 exhibited EA and CA rates exceeding 90.0%.

Conclusion

Based on these findings, we recommend that the AutoMic-i600 system could be a new option for routine AST testing in a clinical setting. Particularly for drug-resistant bacteria and novel antibiotics, detection with AutoMic-i600 may be more reliable, which could further contribute to the prevention and treatment of drug-resistant bacteria.

Epidemiological and clinical characteristics of patients with carbapenem-resistant Enterobacterales in a university hospital of Colombia: Enzyme coproductions in rise

The distribution of carbapenemases in Carbapenem-Resistant Enterobacterales (CRE) has recently undergone a change in our region. According to the Colombian National Institute of Health, there is an increasing prevalence of NDM and NDM-KPC co-producing strains. We carried-out an ambispective cohort study of adult inpatients from Hospital Universitario San Ignacio (2021-2023), infected or colonized with CRE, in which carbapenemases immunochromatographic assay was performed. Out of the 150 patients included in the study, 71.3 % presented with an infection, and carbapenemases were detected in 92.7 % of these cases. Among them, KPC predominated (54 %), while 16.7 % demonstrated enzyme coproductions, mainly KPC-NDM. CRE infected patients had an 18.7 % 30-days mortality, but we could not demonstrate an association between type of carbapenemase and mortality rate (p = 0.82). Logistic regression analysis suggested that ICU admission was independently correlated to fatality (OR 5.08; CI 1.68-16.01). NDM and KPC-NDM presence in CRE poses a public health threat and a therapeutic challenge, with unknown mortality differences according to the carbapenemases pattern. Nevertheless, there was not an association between enzyme type and mortality.

Comparison of carbapenem MIC for NDM-producing Enterobacterales by different AST methods

Introduction

This study compared the performance of MIC test strip (ETEST), automated AST card (Vitek 2) and broth microdilution (BMD) in determining carbapenem susceptibility and MIC values of NDM-producing Enterobacterales.

Methods

NDM-producing Enterobacterales recovered from clinical specimens were included. The presence of blaNDM was confirmed by PCR. Identification of bacterial isolates was done by MALDI-TOF. Phenotypic susceptibility to three carbapenems (ertapenem, imipenem and meropenem) was tested by BMD, ETEST and Vitek 2. MIC values were interpreted in accordance with CLSI M100 (2022 edition). Using BMD as the reference standard, the essential agreement (EA), categorical agreement (CA), very major error (VME) and major error (ME) rates were evaluated.

Results

Forty-seven NDM-producing Enterobacterales isolates were included, 44 of which were Escherichia coli. The EA of Vitek 2 was 97.9% for ertapenem, 25.5% for meropenem and 42.6% for imipenem. Using Vitek 2, there were 0% VMEs across all three carbapenems tested. The EA of ETEST was 53.2% for ertapenem, 55.3% for imipenem and 36.2% for meropenem. The rates of VMEs for ETEST were high too (ertapenem 8.5%, meropenem 36.2%, imipenem 26.1%). The MIC values obtained from Vitek 2 were consistently higher than those from BMD, while MICs from ETEST were consistently lower than those from BMD.

Conclusions

The VME rate for ETEST was unacceptably high when BMD was used as the standard for comparison. Vitek 2 had acceptable EA and CA for ertapenem when BMD was used as the standard for comparison. For meropenem and imipenem, neither of the methods (ETEST, Vitek 2) showed acceptable EA and CA when compared with BMD.

An Ion-Pair Induced Intermediate Complex Captured in Class D Carbapenemase Reveals Chloride Ion as a Janus Effector Modulating Activity

Antibiotic-resistant Enterobacterales that produce oxacillinase (OXA)-48-like Class D β-lactamases are often linked to increased clinical mortality. Though the catalytic mechanism of OXA-48 is known, the molecular origin of its biphasic kinetics has been elusive. We here identify selective chloride binding rather than decarbamylation of the carbamylated lysine as the source of biphasic kinetics, utilizing isothermal titration calorimetry (ITC) to monitor the complete reaction course with the OXA-48 variant having a chemically stable N-acetyl lysine. Further structural investigation enables us to capture an unprecedented inactive acyl intermediate wedged in place by a halide ion paired with a conserved active site arginine. Supported by mutagenesis and mathematical simulation, we identify chloride as a "Janus effector" that operates by allosteric activation of the burst phase and by inhibition of the steady state in kinetic assays of β-lactams. We show that chloride-induced biphasic kinetics directly affects antibiotic efficacy and facilitates the differentiation of clinical isolates encoding Class D from Class A and B carbapenemases. As chloride is present in laboratory and clinical procedures, our discovery greatly expands the roles of chloride in modulating enzyme catalysis and highlights its potential impact on the pharmacokinetics and efficacy of antibiotics during in vivo treatment.