ABSTRACT
Background. The spread of carbapenem resistant Pseudomonas aeruginosa and carbapenemase-producing Enterobacterales (CPE) has had a great impact on morbidity and mortality. COVID-19 pandemic has favoured the selection of these microorganisms because of the excessive and prolonged use of broad-spectrum antibiotics and the outbreaks related to patient transfer between hospitals and inadequate use of personal protective equipment. Therefore, detection is considered essential for their control. Our aim was to compare conventional phenotypic synergy tests and two lateral flow immunoassays for detecting carbapenemases in Enterobacterales and P. aeruginosa. Methods. We analysed 100 carbapenem-resistant Gram-negative bacilli isolates, 80 Enterobacterales and 20 Pseudomonas aeruginosa, (86 isolates producing KPC, NDM, OXA-48, IMP and VIM carbapenemases and 14 non-carbapenemase-producing isolates). We performed a modified Hodge test, boronic acid and ethylenediaminetetraacetic acid (EDTA) synergy tests, and two lateral flow immunoassays: RESIST-4 O.K.N.V (Coris BioconceptR) and NG Test Carba 5R (NG BiotechR). Results. In total, 76 KPC, 7 VIM, 1 NDM, 1 OXA-48 and 1 isolate coproducing KPC + NDM enzymes were included. The concordance of different methods estimated by Kappa index was 0.432 (Standard error: 0.117), thus showing a high variability with the synergy tests with boronic acid and EDTA and reporting 16 false negatives that were detected by the two immunochromatographic methods. Co-production was only detected using immunoassays. Conclusion. Conventional phenotypic synergy tests with boronic acid and EDTA used for detecting carbapenemases are suboptimal and their routine use should be reconsidered. They depend on the degree of enzyme expression and the distance between disks. Lateral flow immunoassay tests are a rapid and cost-effective tool to detect and differentiate carbapenemases, improving clinical outcomes through targeted therapy and promoting infection prevention measures.