Genome-Based Analysis of Genetic Diversity, Antimicrobial Susceptibility, and Virulence Gene Distribution in Salmonella Pullorum Isolates from Poultry in China

Pullorum disease, caused by <i>Salmonella enterica</i> serovar Pullorum (<i>S</i>. Pullorum) infection, is a major pathogenic threat to the poultry industry. In this study, 40 <i>S</i>. Pullorum isolates from seven provinces of China were comprehensively analyzed in terms of antigenic type and antimicrobial susceptibility, and their drug-resistance genes and virulence genes were identified with whole-genome sequencing (WGS). We show that all these isolates were standard antigenic types, with ST92 the predominant genotype (92.5%). Disk diffusion assays revealed high resistance rates to streptomycin (92.5%), ciprofloxacin (82.5%), and ampicillin (80%), and the resistance rates to streptomycin, gentamicin, ampicillin, and cefotaxime were higher in isolates from sick chickens than in those from healthy chickens. In addition, <i>gyrA</i> mutations and eight acquired resistance genes were identified, with <i>aac(6')-Iaa</i> the most prevalent, followed by <i>blaTEM1β</i>, <i>sul2</i>, and the GyrA S83F mutation. The resistance phenotypes to streptomycin, ampicillin, and ciprofloxacin correlated strongly with the presence of the <i>aac(6')-Iaa</i> resistance gene, <i>blaTEM1β</i> resistance gene, and <i>gyrA</i> mutations, respectively. Analysis of the virulence genes showed that the isolates expressed numerous factors associated with secretion systems, including SPI-1 and SPI-2. Overall, this study extends our understanding of the epidemiology and antibiotic resistance of <i>S</i>. Pullorum in China.