Phenotypic and Genotypic Assessment of Carbapenem and Colistin Resistance Patterns in Enterobacterales Isolated at a Tertiary Care Centre, Lucknow

Abstract

Antimicrobial resistance among Enterobacterales has emerged as one of the most significant global public health threats. Carbapenems have traditionally been regarded as the last line of defense against multidrug-resistant Gram-negative infections; however, the rapid dissemination of carbapenem-resistant Enterobacterales (CRE) has markedly reduced their therapeutic effectiveness. Colistin has consequently re-emerged as a salvage therapy, but increasing resistance to colistin has further complicated clinical management. Resistance is mediated by diverse mechanisms, including carbapenemase production (KPC, NDM, VIM, IMP, and OXA-48-like enzymes), porin alterations, efflux pump overexpression, and plasmid-mediated or chromosomal mechanisms affecting colistin susceptibility. Accurate detection of these resistance determinants requires the integration of phenotypic and molecular diagnostic methods. Phenotypic methods such as broth microdilution, modified carbapenem inactivation method (mCIM), Carba NP test, and rapid polymyxin NP test remain valuable in routine laboratories, whereas PCR, multiplex PCR, real-time PCR, whole-genome sequencing, and next-generation sequencing provide rapid and definitive identification of resistance genes. This review summarizes current knowledge regarding the epidemiology, molecular mechanisms, laboratory diagnosis, therapeutic options, and infection prevention strategies for carbapenem-and colistin-resistant Enterobacterales. It also highlights emerging diagnostic technologies and emphasizes the importance of antimicrobial stewardship and genomic surveillance in limiting the spread of these highly resistant pathogens.