Changes in the Phenotypes of spp. in Japanese Broiler Flocks.

infections represent a leading cause of foodborne illnesses; resistance to third-generation cephalosporins (TGCs), which are a first-choice antimicrobial for treating human enteritis, has become a serious public health concern worldwide. Because the consumption of undercooked chicken meat products is a major cause of foodborne salmonellosis in Japan, we conducted three surveys at different periods between 2017 and 2022, with the cooperation of four abattoirs (two in Eastern and two in Western Japan). The first survey was conducted at abattoir A, which is located in Eastern Japan. was detected in 84.4% of broiler flocks tested (27/32); among them, all the TGC-resistant isolates obtained from one farm (farm FA) were identified as Infantis. was recovered from 62.5% of breast meat samples (20/32), with one case suggesting cross-contamination. The second survey was conducted at three other abattoirs to examine the prevalence of TGC-resistant , in both Western (abattoirs B and C) and Eastern (abattoir D) Japan. was detected in 90.6% of broiler flocks examined (29/32). TGC-resistant Infantis was isolated from 2 flocks until 2018 and not thereafter. Subsequently, isolates were identified as TGC-susceptible Schwarzengrund in both regions. The third survey was performed at abattoir A to elucidate whether there were changes in the phenotypes. Of the 11 broiler flocks introduced from farm FA, 10 were positive for (90.9%); all the isolates were Schwarzengrund susceptible to TGC. This study shows that TGC-susceptible Schwarzengrund has replaced the resistant phenotypes among broiler flocks in both Eastern and Western Japan. Although chicken meat products could be cross-contaminated with during the slaughtering process, reducing the prevalence of in broiler flocks remains important to decrease enteritis in humans.