Escherichia coli encoding blaNDM-5 associated with community-acquired urinary tract infections with unusual MIC creep-like phenomenon against imipenem

Abstract Objectives Carbapenemase-producing Escherichia coli are a major clinical concern. The current study aimed to identify NDM-5-producing E. coli associated with community-acquired urinary tract infections (UTIs) co-harbouring extended-spectrum β-lactamases (ESBLs) and showing a phenomenon of imipenem minimum inhibitory concentration (MIC) creep. Methods A total of 973 urine samples were collected from females aged between 18–49 years diagnosed with UTI in Northeast India (June 2014–July 2016). Isolates were identified by standard microbiological methods. The presence of bla NDM and ESBL genes was determined by PCR and sequencing. PCR-based replicon typing was performed. Plasmid stability of all β-lactamase-producers and their transformants was analysed by serial passage, and the MIC creep phenomenon was analysed by studying revertants. Results Among 34 bla NDM-5 -positive E. coli isolates, 21 (61.8%) co harboured bla CTX-M-15 , followed by multiple combinations of genes. This study revealed diverse plasmid types (HI1, I1, FIA + FIB, FIA and Y). The strains showed progressive plasmid loss after 31 passages. Most if the isolates had MICs of 0.5 μg/mL and 1 μg/mL to imipenem, ertapenem and meropenem. However, on studying the MIC creep phenomenon, the MIC was found to be elevated from 0.5 μg/mL to 64 μg/mL and from 1 μg/mL to 128 μg/mL. Analysis of revertants shows that the MIC of most NDM-positive isolates was reduced to 16 μg/mL after the 30th serial passage. Conclusion This study observed a unique phenotype of NDM-producers that has not been reported previously. The observed phenomenon poses a global threat as these pathogens may evade phenotypic screening by routine laboratories.