Antibiotic disk elution method to determine the colistin susceptibility against enterobacterales and non-fermenter bacteria

Colistin minimum inhibitory concentration among Enterobacterales and Non-fermenters was determined using the new susceptibility method, Colistin Broth Disk Elution Method (CBDE), and its sensitivity and specificity. This descriptive cross-sectional study was conducted at Pakistan Railway Hospital, Rawalpindi from October 2020 to August 2021. Gram-negative bacteria were isolated and identified using Gram Stain and standard biochemical profile. Colistin Susceptibility was determined using CBDE and reference methods and then sensitivity and specificity of CBDE with standard reference methods. Essential and Categorical agreements were calculated. A total of 140 Gram-negative isolates were recovered from different specimens. The sensitivity and specificity of CBDE among Enterobacterales were 90.90% and 92.07% and for Pseudomonas aeruginosa 100% and 83.3% and for Acinetobacter baumannii 30% and 50% respectively. CBDE is simple, reliable, and cost effective to determine the colistin susceptibility among Enterobacterales and Pseudomonas aeruginosa while for Acinetobacter baumannii, this procedure is not useful. (author)