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.

Salmonella enterica is a significant zoonotic pathogen, posing a serious public health threat through its presence in the food supply chain, particularly in poultry production facilities. This study aimed to investigate the genetic diversity, antimicrobial resistance (AMR) profiles and phylogenetic relationships of S. enterica serovars isolated from various stages of the broiler supply chain in Harare, Zimbabwe. Whole-genome sequencing was employed to analyse 28 Salmonella isolates from broiler farms, slaughter facilities and retail markets. The overall prevalence of Salmonella was 5.1% out of 552 samples tested. Contamination rates were higher at slaughter facilities, where 11% of 100 samples tested positive and at retail markets, where 20% of 20 samples were contaminated. In contrast, farms had a significantly lower prevalence, with only 3.0% of 432 samples showing Salmonella presence. Eight serovars were identified, with S. enterica subsp. enterica serovar Typhimurium being the most prevalent at 27.6%. Notably, 34.5% of the isolates harboured resistance genes, including fosA3 , fosA7.2 and qnrB19 , and exhibited mutations in the gyrA and parC regions. An extended-spectrum beta-lactamase-producing S. enterica subsp. enterica serovar Kentucky ST198 strain was isolated from retail chicken cuts. All isolates carried virulence genes such as iroC , iroB and sinH , with sodC1 present in 47.4% of the isolates. Approximately 31% of the isolates co-harboured antimicrobial, stress tolerance and virulence genes. Genomic analysis identified distinct sequence types while also revealing identical core SNPs in genomes across various stages of the supply chain. This study highlights the transmission of Salmonella and AMR in the broiler supply chain, emphasizing the urgent need for improved surveillance and intervention strategies to reduce public health risks from contaminated poultry products.