Colistin Insusceptibility in Carbapenem-Resistant Enterobacteriaceae Isolates From a Tertiary Referral Centre

Background Antimicrobial resistance has developed significant importance as a worldwide health concern more so in the 21^st century. This is more specifically observed among the <i>Enterobacteriaceae</i> family, the major group of Gram-negative bacteria. Resistance to carbapenems and colistin antimicrobials from the reserve group, in critical infection treatment poses a substantial therapeutic challenge. This study aims to detect resistance to both carbapenems and colistin in <i>Enterobacteriaceae</i> isolates, emphasizing the importance of monitoring. Materials and methods A laboratory-based study investigated 82 Carbapenem-Resistant <i>Enterobacteriaceae</i> (CRE) isolates from hospitalized patients at Krishna Hospital & Medical Research Centre, Karad, India, for two years (November 2021-November 2023). The Kirby-Bauer disc diffusion method was used to determine the antimicrobial susceptibility following Clinical Laboratory Standards Institute 2022 recommendations. To validate Carbapenem-Resistant <i>Enterobacteriaceae</i> isolates, the Modified Carbapenem Inactivation Method (mCIM) was used, and Colistin resistance was ascertained using Broth Microdilution Susceptibility Testing (BMD). Results Among 309 <i>Enterobacteriaceae</i> isolates, 82 (26.5%) exhibited carbapenem resistance, with 75 confirmed by Modified Carbapenem Inactivation Method (mCIM) testing. For patients in the age group 51-60 years (20%), with men being the most prevalent, the predominance of CRE isolates was from the Intensive Care Unit (44%), mostly from urine samples (34.6%). The most dominant CRE was <i>Klebsiella pneumoniae</i> (62.7%), followed by <i>Escherichia coli</i> (32%). Colistin resistance was found in 14 (18.7%) of CRE isolates, with the highest minimum inhibitory concentration (MIC) at 4 µg/mL (n=10) and 16 µg/mL (n=4). Colistin-resistant isolates (n=10) were sensitive to amikacin (71.4%) and resistant to many antibiotics. Conclusion The extreme rise of colistin-resistant cases among CRE in healthcare settings is a solemn alarm. Among the most effective treatments, aminoglycosides amikacin and netilmicin show the greatest sensitivity against these colistin-resistant CRE infections. The findings stress the difficulties in treating such infections and the dire need for solid antimicrobial stewardship and novel therapeutic strategies.