Isolation, identification and characterization of Salmonella from a parental breeder farm of white broiler and its commercial chickens in northern Jiangsu

Abstract:

[Background] Salmonella is an important zoonotic foodborne pathogen. Therefore, controlling of Salmonella infection in animals and pollution in the food production chain has great significance for livestock production, public health and food safety. [Objective] Studying the infection and epidemic of Salmonella from a parental breeder farm of white broiler and its commercial chickens in northern Jiangsu will provide a reference for the prevention and control of Salmonella. [Methods] A total of 360 samples of cloaca swabs were collected from farms in Taizhou, Suqian, Yancheng and Lianyungang from 2018 to 2019, including 120 samples from parental breeders, their 1 or 2 days old weak commercial broilers and 10 days old commercial broilers, respectively. Then, the Salmonellas were isolated and identified, their drug resistance phenotypes and genotypes were characterized by Kirby-Bauer and PCR methods, and the genetic relationship of the isolates was analyzed by multilocus sequence typing (MLST). [Results] In total, 120 Salmonella strains were isolated, including 3 strains from the parental breeders, 25 strains from the 1 or 2 days old weak commercial broilers and 82 strains from the 10 days old commercial broilers. By using Kirby-Bauer test, all strains were found to be sensitive to antibiotics polymyxin B, imipenem, doxycycline, trimethoprim, tigecycline, florfenicol, cefotaxime and enrofloxacin, and resistant to macrodantin, penicillin, rifampicin, linezolid and vancomycin. Moreover, 80 isolates (72.73%) were sensitive to antibiotic amoxicillin while the other 30 strains (27.27%) were resistant to it. The drug-resistant genes analyzed by PCR showed that blaTEM existed in all isolates, but not other common resistance genes. The ST type of all Salmonella isolates in this study was identified as ST11 based on the MLST typing and sequencing results of 7 pairs of housekeeping genes. Collectively, out data demonstrate that the phylogenies of these Salmonella isolates are very similar. [Conclusion] Salmonella infections occurred in the commercial broilers seemed to be caused by vertical transmission from the same herds of parental breeders. This study provided a reference for the prevention and control of Salmonella in white broiler farms in this area.