Real-time PCR method for Salmonella spp. targeting the stn gene

AIM: To develop a real-time PCR assay for Salmonella spp. targeting the stn gene. METHODS AND RESULTS: The presence of stn in the Salmonella bongori genome was found by a BLAST with Salmonella enterica stn sequence. Manual alignment of stn sequences showed that Salm. bongori had 88% sequence identity with Salm. enterica. Two primers (stnL-433 and stnR-561) and a probe (stnP-452) were designed to target conserved regions in stn and meet the requirements of a 5'-nuclease assay. The primers and probe were evaluated against 353 isolates, including 255 Salm. enterica representing 158 serotypes, 14 Salm. bongori representing 12 serotypes and 84 non-Salmonella representing 56 species from 31 genera. All isolates were correctly identified, with the exception of three isolates of Citrobacter amalonaticus, which gave false positives. The limit of detection with cultured Salmonella was 3 CFU per reaction. CONCLUSIONS: The stn real-time PCR method had 100% inclusivity, 96.4% exclusivity and a level of detection of 3 CFU per reaction for cultured Salmonella spp. SIGNIFICANCE AND IMPACT OF THE STUDY: The study showed that stn is present in Salm. bongori and is a valid target for both species of Salmonella. The Salmonella s tn real-time PCR is a useful method for identifying Salmonella spp.     

Effect of cloned Salmonella typhimurium enterotoxin on rabbit intestinal motility

Abstract We analysed the small intestine myoelectric responses of anesthetized New Zealand albino rabbits to Escherichia coli lysates containing an enterotoxin cloned from Salmonella typhimurium . Migrating action potential complex, which consisted of rapid bursts of action potentials and secretion of fluid, was observed only in ileal loops injected with the enterotoxin-containing lysate. Migrating action potential complex produced by Stn usually propagated aborally, which was typical of cholera toxin, but orad or bidirectional propagation occurred from a single point of origin when activity was intense. Gell lysates from an E. coli clone containing vectors alone, as well as proximal control segments injected with phosphate-buffered saline, gave neither a change in motility nor fluid secretion. These results show that Stn caused dramatic changes in intestinal motility and substantial fluid production.