Antimicrobial resistance and mcr-1 gene in Escherichia coli isolated from poultry samples submitted to a bacteriology laboratory in South Africa

BACKGROUND AND AIM: Antimicrobial resistance (AMR) and recently mobilized colistin resistance (mcr-1) associated colistin resistance among Escherichia coli isolates have been attributed to the overuse of antimicrobials in livestock production. E. coli remains an important pathogen, often associated with mortality and low carcass weight in poultry medicine; therefore, the need to use antimicrobials is common. The study aimed to determine the AMR profile and presence of mcr-1 and mcr-2 genes in avian pathogenic E. coli from poultry samples tested at a bacteriology laboratory for routine diagnosis. This is a first step in understanding the effectiveness of mitigation strategies. MATERIALS AND METHODS: Fifty E. coli strains were assessed for resistance against ten antimicrobial drugs using broth microdilution. All isolates with a colistin minimum inhibitory concentration (MIC) of 2 µg/mL were analyzed for the presence of mcr-1 and mcr-2 genes by employing the polymerase chain reaction. For each isolate, the following farm information was obtained: farm location, type of farm, and on-farm use of colistin. RESULTS: Sixty-eight percent of the strains were resistant to at least one antimicrobial; 44% were multiple drug-resistant (MDR). Most E. coli isolates were resistant to doxycycline (44%), trimethoprim-sulfamethoxazole (38%), ampicillin (32%), and enrofloxacin (32%). None of the E. coli strains was resistant to colistin sulfate (MIC90 of 2 µg/mL). Only one E. coli isolate held the mcr-1 gene; none carried the mcr-2 gene. CONCLUSION: Resistance among E. coli isolates in this study was fairly high. Resistance to commonly used antimicrobials was observed, such as doxycycline, trimethoprim-sulfamethoxazole, and enrofloxacin. Only a single E. coli strain carried the mcr-1 gene, suggesting that mcr-1 and mcr-2 genes are common among isolates in this study. The prevalence of AMR, however, suggests that farmers must implement standard biosecurity measures to reduce E. coli burden, and antimicrobial use to prolong the efficacy life span of some of these drugs.