Decreasing trend of β-lactam resistance in Salmonella isolates from broiler chickens due to the cessation of ceftiofur in ovo administration

Ceftiofur, a third-generation cephalosporin antimicrobial, was used in Japanese hatcheries for many years before 2012. We continue to study Salmonella in broilers and their antimicrobial resistance. The current study aimed to express how the cessation of ceftiofur affects the antimicrobial resistance of Salmonella isolated from broiler chickens in Kagoshima Prefecture, Japan in 2017 and 2018. A total of 274 Salmonella isolates were recovered from 1535 cecal content samples obtained from 96 broiler flocks over years 2017 and 2018. Among the S. enterica isolates, the predominant serovars were S. Manhattan (128/274, 46.7%), S. Schwarzengrund (120/274, 43.8%), and S. Infantis (26/274, 9.5%). The isolates showed a high proportion of antimicrobial resistance for oxytetracycline, sulfamethoxazole, and streptomycin. However, the β-lactam resistance rates were significantly decreased (p < 0.01) in 2017, while no β-lactam resistant isolates detected in 2018. The highlight of this study was the complete disappearance of β-lactam resistance in Salmonella isolates from broiler chicken in Kagoshima, Japan.