Prevalence of Antibiotic-Resistant Salmonella in Fish in Guangdong, China

Introduction: This study examines fish from freshwater aquaculture operations in Guangdong Province, China, to determine the prevalence of antibiotic-resistant Salmonella isolates. This information can help identify risks of human exposure to Salmonella and guide decisions of whether to include farmed fish samples in routine food surveillance for Salmonella. Methods: One hundred live freshwater-farmed finfish were sampled from several stalls at two wholesale and four retail markets in Guangzhou from June to July 2008. Isolation and antibiotic sensitivity testing was done according to the U. S. FDA Bacteriological Analytical Manual. Antibiotic sensitivity testing was done using the Kirby Bauer disk diffusion method. Results: All five Salmonella isolates were susceptible to neomycin, cefotaxime, and cefepime and resistant to erythromycin and penicillin. The most resistant isolate was susceptible to 7 of the 16 antibiotics tested. Discussion: The estimated prevalence of Salmonella is 5% (95% CI: 2-11%) in live finfish from markets in Guangzhou, China. All five isolates were not susceptible to three or more antibiotics. Three of the five isolates had decreased susceptibility to nitrofurantoin, suggesting illegal use of nitrofurans in food animal production, and surveillance of resistance to this class of antibiotics is warranted. We suggest aquaculture-producing countries where there may be high antibiotic use to add farmed fish products to the list of foods they include in Salmonella surveillance. This would help evaluate human health risks posed by antibiotic-resistant bacteria in farmed fish products.