Molecular Characteristics and Antimicrobial Resistance of Serovar Schwarzengrund from Chicken Meat in Japan.

Our previous study revealed that 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 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% ( < 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, , and , significantly decreased from 100% in 2008 to 47.1% in 2015-2019 ( < 0.001). A 1.0-kb class 1 integron containing , harbored by 78 isolates, was different from that reported in globally distributed Schwarzengrund strains (1.9 kb, containing the 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 Schwarzengrund, which contaminates chicken meat in Japan, shares a common ancestor regardless of the product district from 2008 to recent years. Moreover, Schwarzengrund ST241 may have spread from western to eastern Japan.