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The antibiotic susceptibility of fecal Escherichia coli isolates from commercial-layer and free-range
chickens in Arusha district, Tanzania were compared. All the chickens were raised by individual
households, but commercial-layer chickens were purchased from commercial vendors, whereas no
systematic breeding system was used to produce free-range chickens. A total of 1,800 E. coli isolates
(1,200 from commercial-layer chickens and 600 from free-range chickens) were tested for susceptibility
to 11 antibiotics by breakpoint assays. All E. coli isolates were susceptible to gentamicin, ceftazidime
and cefotaxime. Isolates from commercial-layer chickens had a high prevalence of resistance (32.4-
74.5%) for amoxicillin, ampicillin, ciprofloxacin, tetracycline, streptomycin, trimethoprim and
sulfamethoxazole, while the prevalence of resistance to these antibiotics was lower (7-31.5%) for freerange
chickens (P<0.05). Both groups had a similar prevalence of resistance to chloramphenicol (1.17-
1.5%; P>0.05). For antibiotic resistant strains, 64.1 and 91.5% of free-range and commercial-layer
isolates, respectively, were resistant to ≥ 2 antibiotics. Commercial-layer chickens harbored
significantly more resistant E. coli isolates (P<0.001) than free-range chickens, consistent with more
exposure to antibiotics when compared with free-range chickens. Efforts should be directed towards
motivating household owners to limit the use of antibiotics when they are investing in these breeds. |
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