Antimicrobial Susceptibility Profiles of Extended-Spectrum β-Lactamase-Producing Escherichia coli Isolated From Intensively Reared and Free-Range Chickens in Selected Districts of Zambia.

BACKGROUND

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in poultry is an emerging One Health concern, yet comparative data on intensive versus free-range systems in sub-Saharan Africa remain sparse.

OBJECTIVES

To compare the prevalence, susceptibility profiles and β-lactamase gene content of ESBL-producing E. coli from intensively reared and free-range chickens in Central Province, Zambia.

METHODS

In a cross-sectional study (March-April 2021), 112 pooled faecal samples (56 per production system; 10 birds per sampling point) were collected across seven veterinary camps in Kabwe and Kapiri Mposhi districts and processed within 24 h. Presumptive ESBL E. coli was isolated on MacConkey agar with 2 mg/L cefotaxime and identified biochemically. Susceptibility to 11 antimicrobials was tested by Kirby-Bauer disc diffusion per CLSI M100 (2020), and ESBL production was confirmed by combination-disc synergy. blaCTX-M, blaTEM and blaSHV were detected by multiplex PCR. Proportions were compared using Fisher's exact test with 95% Wilson confidence intervals (CIs).

RESULTS

ESBL-producing E. coli was recovered from 13/112 pooled samples (11.6%, 95% CI: 6.9%-18.9%), with no difference between intensively reared (7/56, 12.5%) and free-range (6/56, 10.7%) chickens (p = 1.00). All 13 isolates were multidrug-resistant, with the highest resistance to tetracycline and cefotaxime (both 100%), streptomycin (84.6%) and sulfamethoxazole-trimethoprim (69.2%). blaCTX-M was present in all 13 isolates, blaTEM in 4 (30.8%) and blaSHV in 1 (7.7%), with co-carriage in 5 isolates.

CONCLUSIONS

Multidrug-resistant, blaCTX-M-driven ESBL E. coli circulates at comparable levels in both production systems, consistent with environmental dissemination. Integrated One Health surveillance and antimicrobial stewardship are warranted.