Unveiling colistin resistance in extensively drug-resistant microorganisms among ICU patients of tertiary care hospital Karachi, Pakistan

Objective: To determine the prevalence of extensively drug-resistant (XDR) microorganisms in the intensive care unit (ICU) of a tertiary care hospital in Karachi and to identify the presence of colistin resistance (CLR) among these XDR isolates. Material and Methods: A cross sectional study was carried out in the ICU of a tertiary care hospital from August 2022 to February 2023 and various clinical samples of XDR Gram negative bacilli (GNB) were collected from ICU. These specimens were processed by following the guidelines established by the Clinical and Laboratory Standards Institute (CLSI), Agar and broth microdilution methods were used to assess the colistin susceptibility of XDR isolates. Results: The study focused on 100 extensively drug-resistant (XDR) specimens. K. Pneumoniae dominated (32%), followed by E. coli (23). Among the 100 XDR, 89% were colistin susceptible, and 11% were resistant, tested by agar and broth microdilution. Of the 11% CLR, P. aeruginosa was most common, with the highest resistance in urine specimens. Colistin resistance was highest for P. aeruginosa (45%), followed by A. baumannii (18%), E. coli (18%), K. Pneumoniae (9%), and K. oxytoca (9%). CLR isolates were mainly (27%) from urine. Conclusion: Prolonged hospital stays and antibiotic pressure can lead to CLR development. Labs should monitor XDR closely, implementing measures to minimize antibiotic resistance. Controlling colistin resistance through stewardship is crucial. Keywords: Extensively drug resistant, Colistin resistant, Minimum inhibitory concentration, Nasobronchial lavage