A novel method for measuring phenotypic colistin resistance in Escherichia coli populations from chicken flocks.

A novel method for measuring phenotypic colistin resistance in Escherichia coli populations from chicken flocks. Appl Environ Microbiol. 2020 Dec 18;: Authors: Nguyen NT, Phuong Yen NT, Ky Thien NV, Van Cuong N, Kiet BT, Campbell J, Thwaites G, Baker S, Geskus RB, Carrique-Mas J Abstract Colistin is extensively used in animal production in many low- and middle-income countries. There is a need to develop methodologies to benchmark and monitor changes in resistance among mixed commensal bacterial populations in farms. We aimed to evaluate the performance of a broth microdilution method based on culturing a pooled Escherichia coli suspension (30-50 organisms) obtained from each sample. To confirm the biological basis and sensitivity of the method, we cultured 16 combinations of one colistin-susceptible and one mcr-1 encoded colistin-resistant E. coli in the presence of 2mg/L colistin. Optical density (OD600nm) readings over time were used to generate a growth curve, and these values were adjusted to the values obtained in the absence of colistin (adjusted Area Under the Curve, AUCadj). The median limit of detection was 1 resistant in 104 susceptible colonies [1st - 3rd quartile, 102:1 -105:1]. We applied this method to 108 pooled faecal samples from 36 chicken flocks from the Mekong Delta (Vietnam), and determined the correlation between this method and the prevalence of colistin resistance in individual colonies harvested from field s...
Source: Applied and Environmental Microbiology - Category: Microbiology Authors: Tags: Appl Environ Microbiol Source Type: research