Virulence determinants and multidrug resistance of emerging Salmonella enterica subspecies salamae in broiler chickens: a potential zoonotic concern

Salmonella is a relevant zoonotic food-borne pathogen worldwide. Consequently, a significant amount of research has been focused on Salmonella enterica serovars over a substantial period of time. By far, investigating non-enterica subspecies in food-producing animals is an overlooked issue. Therefore, this study aimed to examine the prevalence, antimicrobial resistance, and virulence determinants of emerging Salmonella subspecies in broiler chickens in Egypt. Overall, salmonellae were identified in 19 out of 240 broiler chickens. This study revealed an unexpected distribution of serovars, with S. enterica subsp. salamae being identified in 31.6% of broilers, trailing behind S. Enteritidis (63.2%) and followed by S. Infantis (5.3%). Multidrug resistance accounted for 73.7% of the isolates, with four isolates of S. enterica subsp. salamae exhibiting a multiple antibiotic resistance index (MARI) greater than 0.2. A total of 19 antibiotic resistance and 7 virulence genes were investigated among 19 Salmonella isolates, showing varying frequencies. All six S. enterica subsp. salamae strains carried tetA, int1, and blaTEM, as well as six virulence genes (stn, spiA, sopB, ompF, ompA, and pefA), with spvB detected in five. Furthermore, a phylogenetic analysis of the Salmonella enterotoxin (stn) gene from two S. enterica subsp. salamae isolates revealed genetic similarities to isolates identified in wild birds and humans, highlighting their zoonotic potential. These outcomes shed light on the emerging MDR and virulent S. enterica subsp. salamae, which have raised a potential public health threat and necessitate strict monitoring and surveillance of non-enterica subspecies in the poultry sector.