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

Nontyphoidal <i>Salmonella</i> spp. potentially lead to economic loss, thereby threatening the poultry industry; moreover, they are major pathogens that can cause human illness. In this study, <i>Salmonella</i> 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. <i>Salmonella</i> were isolated from 35 (26.5%) farms, and the most frequently detected serovar was <i>Salmonella enterica</i> serovar Enteritidis, detected in 19 (14.4%) farms, followed by <i>Salmonella enterica</i> serovars Typhimurium (4 farms, 3.0%), <i>S</i>. Senftenberg (3 farms, 2.3%), <i>S</i>. Agona (2 farms, 1.5%), <i>S</i>. Montevideo (2 farms, 1.5%), <i>S</i>. Infantis (2 farms, 1.5%), <i>S</i>. Thompson (2 farms, 1.5%), and <i>S</i>. Bareilly (1 farm, 0.8%) (<i>P</i> < 0.05). In particular, <i>S</i>. 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 (<i>P</i> < 0.05), and the prevalence of multidrug resistance showed significant differences among the five integrated operations (<i>P</i> < 0.05). <i>S</i>. Enteritidis was divided into 18 pulsed-field gel electrophoresis pattern types; however, confirming the epidemiological relationship proved challenging. Moreover, 9 (14.5%) among 62 <i>S</i>. Enteritidis isolates harbored 2 kinds of β-lactamase genes, <i>bla</i>_TEM-1 (2 isolates) and <i>bla</i>_CTX-M-55 (7 isolates), and 4 (6.5%) <i>S</i>. 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 <i>S</i>. Enteritidis isolates, but the <i>cbtB</i> and <i>pefA</i> genes were only detected in 2 isolates (3.2%) and 1 isolate (1.6%), respectively. This study indicates that various <i>Salmonella</i> spp., including <i>S</i>. Enteritidis and <i>S</i>. Typhimurium, are persistent in commercial broiler farms via vertical or horizontal transmission.