Rapid detection of carbapenem resistance: targeting a zero level of inadequate empiric antibiotic exposure?

Development and Validation of a Multiplex Real-Time PCR Assay for Rapid Screening of Main Carbapenemase Genes in Clinical Isolates and Surveillance Samples

BACKGROUND/OBJECTIVES

Carbapenem-resistant Enterobacterales, largely due to carbapenemase production, are significant public health threats, which compromise treatment with key β-lactam antibiotics. Early detection is essential for guiding therapy and controlling spread. This study describes the design, optimisation and validation of a multiplex real-time PCR for the screening of the most frequent carbapenemases in our area.

METHODS

Primers and probes targeted at genes encoding carbapenemases blaKPC, blaIMP, blaVIM, blaNDM and blaOXA-48-group were designed and adapted for the development, and in silico and experimental validation of a single-tube real-time PCR.

RESULTS

A good linear correlation between the fluorescence values in the real-time PCR and the log10 of bacterial concentration of each carbapenemase-containing bacterial suspension was observed (R2 > 0.98). The limit of detection was 2-15, 16-256, 42-184, 4-42, 42-226 CFU/reaction of VIM-, IMP-, NDM-, KPC- and OXA-48-carbapenemase-containing bacteria, respectively. Intra-assay coefficient of variation for the mean Ct values ranged from 0.99% for OXA-48 to 3.34% for KPC. Inter-assay variability remained below 7%. Real-time PCR tested on bacterial isolates yielded 100% sensitivity and specificity. Analysis of rectal swabs using extracted DNA and a DNA extraction-free protocol showed good concordance with culture-based phenotypic methods. Additionally, the molecular method could detect all targets, except for one sample where only the DNA extraction-free protocol detected NDM.

CONCLUSIONS

The assay offers a rapid, sensitive and specific method for the screening of major carbapenemase genes, providing an effective tool for surveillance and infection control in clinical settings. The DNA extraction-free protocol converts this method into a good alternative for screening in 24/7 clinical laboratories. Further multiplexing to target other resistance genes, on demand, could add potential benefits to this laboratory-developed method.

What Healthcare Workers Should Know about Environmental Bacterial Contamination in the Intensive Care Unit

Intensive care unit- (ICU-) acquired infections are a major health problem worldwide. Inanimate surfaces and equipment contamination may play a role in cross-transmission of pathogens and subsequent patient colonization or infection. Bacteria contaminate inanimate surfaces and equipment of the patient zone and healthcare area, generating a reservoir of potential pathogens, including multidrug resistant species. Traditional terminal cleaning methods have limitations. Indeed patients who receive a bed from prior patient carrying bacteria are exposed to an increased risk (odds ratio 2.13, 95% confidence intervals 1.62-2.81) of being colonized and potentially infected by the same bacterial species of the previous patient. Biofilm formation, even on dry surfaces, may play a role in reducing the efficacy of terminal cleaning procedures since it enables bacteria to survive in the environment for a long period and provides increased resistance to commonly used disinfectants. No-touch methods (e.g., UV-light, hydrogen peroxide vapour) are under investigation and further studies with patient-centred outcomes are needed, before considering them the standard of terminal cleaning in ICUs. Healthcare workers should be aware of the role of environmental contamination in the ICU and consider it in the broader perspective of infection control measures and stewardship initiatives.