PCR PRIMER EFFICACY IN DETERMINING SALMONELLA PREVALENCE IN SOUTHERN ARIZONA SHELTER DOGS AND FERAL CATS

Abstract

Salmonella is an enteric pathogen that can be transmitted zoonotically between humans and animals, including companion cats and dogs. One of the virulence factors that enables colonization of the gastrointestinal tract is the type III secretion system, as encoded in Salmonella Pathogenicity Island 1 (SP-1), and one of the component proteins of this virulence factor is the Invasive A protein (InvA). InvA is encoded by the invA gene, which is highly conserved within Salmonella species, so amplification of this gene through polymerase chain reaction (PCR) is often used to detect clinical isolates of Salmonella in humans, animals, and contaminated food and water sources. This study utilized the invA PCR to determine the prevalence of Salmonella in shelter dogs and feral cats. Additionally, PCR detection efficacy was studied by utilizing different primer sets and the additive bovine serum albumin (BSA). Three different primer sets, coined the "MC" primer set, "KC" primer set, and "VO" primer set, were tested. The MC primer set detected the invA gene in 16 of 58 canine fecal samples and 6 of 56 feline fecal samples, the KC primer did not detect the invA gene in any canine fecal sample, and the VO primer set detected the invA gene in 7 of 58 canine fecal samples. It was discovered that the MC primer set was able to detect the invA gene at a lower DNA concentration than the other two, which could contribute to the higher frequency of positive results obtained with that primer set. The effects of BSA addition were observed in sample groupings from shelter dogs and feral cats that were initially positive or negative for the invA gene in their first PCR, where the presence of BSA influenced PCR results from the original samples. The addition of BSA caused 1 sample from both the canine and feline fecal samples that had initially returned as negative to be positive for the invA gene; however, 1 sample from both the canine and feline fecal samples that had initially returned as positive was not positive in the PCR with BSA. PCR is a sensitive and specific tool to confirm the presence of invA, as indicative of Salmonella, and appropriate adjustments, regarding the primer set characteristics and reaction mixture additives, should be considered. Optimizing the PCR conditions will maximize the reliability of PCR as a diagnostic tool to confirm Salmonella diagnoses and to guide treatment and preventative strategies.