Prevalence and Characteristics of Salmonella from a Laying Hen Production Chain in Jiangsu Province, China

Salmonellosis is a significant zoonotic and foodborne disease caused by Salmonella. As a primary reservoir, poultry infections can result in decreased survival rates, diminished production performance and contamination of poultry products, thereby posing a serious threat to the sustainable development of poultry farming and human health. In this study, a total of 979 samples were collected from a laying hen production chain, and 84 Salmonella strains were isolated, with an isolation rate of 8.58% (84/979). Among these, 54 isolates (11.2%) were from commercial house samples, followed by nine isolates (10.8%) from market samples, 10 isolates (5.88%) from hatchery samples, and 11 isolates (4.55%) from breeder house samples. Six different serotypes were identified, with Salmonella enterica serovar Enteritidis (S. Enteritidis) being the predominant serotype (41.7%), followed by Salmonella enterica serovar Typhimurium (S. Typhimurium) (22.6%) and Salmonella enterica serovar Infantis (S. Infantis) (21.4%). The S. Enteritidis was distributed in various production stages in the laying hen production chain. Among the 16 antibiotics tested, 30 selected strains exhibited 100% resistance to nalidixic acid (NAL) and ciprofloxacin (CIP), attributed to mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene. Following this, the resistance rates for ampicillin (AMP), amoxicillin–clavulanate (AMC), and streptomycin (STR) were 56.7%. Antimicrobial resistance genotypes were consistent with the drug resistance phenotype. Whole genome sequencing (WGS) phylogenetic analysis based on core genome single nucleotide polymorphism (cgSNP) revealed that Salmonella can spread across various stages of the laying hen production chain, posing a potential threat to human health. Furthermore, 165 virulence-associated genes were identified among the investigated isolates, indicating a highly conserved virulence repertoire. This study investigates the prevalence of Salmonella within a laying hen production chain, providing a scientific foundation for the effective prevention and control of Salmonella infection.