Dissemination of extended-spectrum beta-lactamase-producing Escherichia coli in poultry in Zimbabwe

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli are resistant to the critically important third- and fourth-generation cephalosporin antibiotics and present a risk to animal and human health. In Zimbabwe, there is an evidence gap concerning the prevalence and diversity of ESBL-producing E. coli in poultry. In this study, we screened for ESBL-E. coli at farms (n=50) and markets (n=10) using MacConkey agar supplemented with 4 µg ml−1 ceftriaxone. ESBL-E. coli were detected at every market and at 21 farms, giving a farm-level prevalence of 42%. Seventy isolates were obtained and tested for antimicrobial susceptibility, whilst 69 of these were further analysed by whole-genome sequencing. A total of eight distinct bla CTX-M variants were identified, and 69 out of 70 isolates were multidrug-resistant. Genomic analysis revealed evidence for clonal expansion of an ESBL-producing clone and horizontal gene transfer via plasmids being responsible for the dissemination of ESBL-E. coli. Geographic Information System mapping was used to visualize the distribution of the ESBL-producing clones. For example, ST1141 isolates were clonal, having a highly conserved core genome, and harboured bla CTX-M-15 and 11 additional antimicrobial resistance genes on a ~338 kbp IncHI2 plasmid which was not present in other isolates. This clone was present at nine farms. In contrast, a conserved ~93 kbp IncFII plasmid harbouring bla CTX-M-55 was present in isolates from three different multilocus sequence types obtained from six farms. This study provides insight into the burden and distribution of ESBL-E. coli at poultry farms in Zimbabwe and provides molecular genetic evidence for clonal expansion and plasmid transfer as being important mechanisms for the dissemination of ESBL-E. coli in this setting. This study underscores the importance of adopting measures, such as prudent antimicrobial use and farm biosecurity, that can limit the development and dissemination of ESBL-producing E. coli.