Paratyphoid Salmonella Serovars in Chickens: Molecular Detection of Virulence and Antimicrobial Resistance Genes

Paratyphoid salmonellosis is a serious disease that threatens the poultry industry worldwide, besides its public health hazard. The aims of this study were characterization of paratyphoid Salmonella spp. in chicken flocks of some Egyptian governorates, demonstration of the antimicrobial susceptibility of the isolated Salmonella spp., and detection of some virulence genes and antibiotic resistance genes using recent molecular techniques. A total of 238 organ samples were collected from 52 broiler, layer, and breeder chicken flocks, representing 9 Egyptian governorates. Conventional characterization of Salmonella isolates revealed a total isolation rate of 56.3% (134/238). Moreover, the isolation rates of Salmonella spp. were (49/79; 62%), (47/81; 58%), (10/18; 55.5%), (9/20; 45%), (2/6; 33.3%), (2/3; 66.7%), and (15/82; 53.6%) from liver, yolk sac, heart, spleen, caecum, ovary, and dead-in-shell embryos, respectively. A total of 32/238 (13.44%) isolates of Salmonella were found. Serological identification revealed presence of S. enteritidis (21.9%), S. kentucky (15.6%), S. typhimurium (12.5%), S. molade (12.5%), S. takoradi (9.4%), S. wingrove (6.3%), S. infantis (6.3%), S. tsevie (6.3), S. shangani (3.1%), S. bargny (3.1%), and S. papuana (3.1%). All Salmonella strains (32/32; 100%) were resistant to streptomycin, while almost all of them (31/32; 96.9%) were susceptible to meropenem. The amplification of 16S rRNA gene of Salmonella isolates using uniplex polymerase chain reaction (PCR) generated a specific Salmonella product of approximately 550 base pair. The multiplex PCR revealed presence of invA (100%), stn (65.6%), and sopB (40.6 %) virulence-associated genes as well as aadA1 (100%), blaTEM (59.4%), aadB (18.75%), and sul1 (28.1%) antibiotic resistance genes. In conclusion, virulent paratyphoid Salmonella spp. are circulating in the Egyptian flocks, causing economic losses. Additionally, they became resistant to the most commonly used field antibiotics. Therefore, regular molecular surveillance studies on the circulating Salmonella spp. and their resistance to the used antibiotics are of significant importance.