Characterization of Salmonella spp. isolated from chickens in Central China

Background Salmonellais an important zoonotic pathogen, and chickens are one of its main hosts. Every year,Salmonellainfections pose a serious threat to the poultry industry in developing countries, especially China. In this study, a total of 84Salmonellaisolates recovered from sick and healthy-looking chickens in central China were characterized by serotyping, MLST-based strain typing, presence of potential virulence factors, and antimicrobial resistance profiles. Result Data showed that the main serotypes ofSalmonellaisolates in central China wereSalmonella entericaserovar Gallinarum biovar Pullorum, Salmonella entericaserovar Gallinarum biovar Gallinarum,Salmonella entericaserovar Enteritidis andSalmonella entericaserovar Typhimurium, and among them,S. Pullorum was the dominant type in both sick and healthy-looking chickens, accounting for 43.9 and 46.5%, respectively, whileS. Enteritidis was only found in healthy-looking chickens. All isolates exhibited higher resistance rates to ampicillin (97.6%), tetracycline (58.3%) and colistin (51.2%), and among these isolates, 49.5% were resistant to more than three drugs in different combinations.S. Enteritidis was the most severe multidrug-resistant serotype, which showed higher resistance rates to colistin, meropenem and ciprofloxacin. Multilocus sequence typing (MLST) revealed thatS. Gallinarum andS. Enteritidis isolates were clustered in clade 1, which belonged to two and one STs, respectively. AllS. Typhimurium isolates were clustered in clade 3, and belonged to three STs. However,S. Pullorum were distributed in three clades, which belonged to 7 STs. Twenty-seven virulence-associated genes were detected, and expectedcdtB, which was absent in all the isolates, the other 26 genes were conserved in the closely relatedSalmonellaserogroup D (S. Enteritidis,S. Pullorum, andS. Gallinarum). Conclusion Salmonellaserogroup D was the major subgroup, andS. Pullorum was the most common type in sick and healthy-looking chickens in central China. Drug resistance assays showed serious multiple antimicrobial resistances, andS. Enteritidis was the most severe drug-resistant serotype. MLST showed that there was correlation between serotypes and genotypes in mostSalmonellaisolates, exceptS. Pullorum, which showed complicated genetic diversity firstly. These results provide important epidemiological information for us to controlSalmonellain chickens.