RESUMO
Our previous study revealed that Salmonella enterica serovar Schwarzengrund-contaminated areas of broiler chickens have expanded from West Japan to East Japan. The present study investigated the antimicrobial resistance and molecular characteristics of 124 S. Schwarzengrund isolates obtained from chicken meat produced in East and West Japan from 2008 to 2019. Comparing the isolates obtained in 2008 and 2015-2019, an increase in the proportion of those resistant to kanamycin [51.4-89.7% (p < 0.001)] was observed. In contrast, the proportion of isolates resistant to both streptomycin and tetracycline and those that harbored a 1.0-kb class 1 integron, aadA1, and tetA, significantly decreased from 100% in 2008 to 47.1% in 2015-2019 (p < 0.001). A 1.0-kb class 1 integron containing aadA1, harbored by 78 isolates, was different from that reported in globally distributed S. Schwarzengrund strains (1.9 kb, containing the dfrA12-aadA2 gene cassette). Twenty-five isolates from different product districts and years of isolation were typed as sequence type (ST) 241 with multilocus sequence typing. Our results suggest that S. Schwarzengrund, which contaminates chicken meat in Japan, shares a common ancestor regardless of the product district from 2008 to recent years. Moreover, S. Schwarzengrund ST241 may have spread from western to eastern Japan.
RESUMO
The effects of climatic elements on Salmonella contamination of chicken meat were investigated. Logistic regression analysis was performed to evaluate the association between Salmonella isolation, for 240 chicken samples purchased from March 2015 to February 2017, and climatic elements, over 65 days of chicken rearing. Salmonella was isolated from 143 samples (59.6%), and the most dominant serovars identified were Infantis (77/240, 32.1%) and Schwarzengrund (56/240, 23.3%). Previous studies have reported S. Schwarzengrund contamination of broiler chickens only in western Japan; however, in the present study, S. Schwarzengrund was also isolated from meat produced in eastern Japan-20% (12/60) in the C prefecture to 36.4% (8/22) in the Y prefecture-suggesting that S. Schwarzengrund-contaminated areas have expanded towards eastern Japan. Air temperature showed a significant negative association with S. Schwarzengrund isolation for chicken meat produced during periods with rising temperature (spring and summer) [odds ratio (OR), 0.894 to 0.935; P<0.01]. Moreover, the risk of S. Schwarzengrund contamination of chicken meat was higher during spring (OR, 3.951; P=0.008) and winter (OR, 4.071; P=0.006) than during summer. Effects of climatic elements and differences in contamination risk across seasons were not observed for any Salmonella serovars and only S. Infantis, which could be attributed to differences in transmission patterns and vehicles among Salmonella serovars. These findings are valuable for understanding the dynamics of S. Schwarzengrund dissemination in broiler farms.
