Characteristics of Salmonella spp. from Chickens That Died Within One Week of Age in Commercial Farms of Integrated Broiler Operations in South Korea

Nontyphoidal Salmonella spp. potentially lead to economic loss, thereby threatening the poultry industry; moreover, they are major pathogens that can cause human illness. In this study, Salmonella were isolated from the internal organs of chickens that had died within one week of age in 132 commercial farms of five integrated broiler operations. Salmonella were isolated from 35 (26.5%) farms, and the most frequently detected serovar was Salmonella enterica serovar Enteritidis, detected in 19 (14.4%) farms, followed by Salmonella enterica serovars Typhimurium (4 farms, 3.0%), S. Senftenberg (3 farms, 2.3%), S. Agona (2 farms, 1.5%), S. Montevideo (2 farms, 1.5%), S. Infantis (2 farms, 1.5%), S. Thompson (2 farms, 1.5%), and S. Bareilly (1 farm, 0.8%) (P, 0.05). In particular, S. Enteritidis was identified on farms (4.5%–22.2%) of all five operations. The prevalence of resistance to nalidixic acid (97.7%–100%) was significantly higher than that of resistance to other antimicrobials (0.0%–44.4%) in all five operations (P, 0.05), and the prevalence of multidrug resistance showed significant differences among the five integrated operations (P, 0.05). S. Enteritidis was divided into 18 pulsed-field gel electrophoresis pattern types; however, confirming the epidemiological relationship proved challenging. Moreover, 9 (14.5%) among 62 S. Enteritidis isolates harbored 2 kinds of b-lactamase genes, bla_TEM-1 (2 isolates) and bla_CTX-M-55 (7 isolates), and 4 (6.5%) S. Enteritidis isolates harbored 2 kinds of integrase genes: class 1 integron (2 isolates) and class 2 integron (2 isolates). Most of the 20 virulence genes tested were detected in more than 93.5% of S. Enteritidis isolates, but the cbtB and pefA genes were only detected in 2 isolates (3.2%) and 1 isolate (1.6%), respectively. This study indicates that various Salmonella spp., including S. Enteritidis and S. Typhimurium, are persistent in commercial broiler farms via vertical or horizontal transmission.