INVESTIGATION OF VIRULENT AND TOXIN GENES EXPRESSION IN SOME SALMONELLA SEROVARS

, , ABSTRACT : Samples collected from patient stool during their course of investigation at hospitals ministry of health, Egypt as well as solid and liquid food samples collected from local markets were examined for presence of Salmonella spp. Isolation and serological identification showed that 92.5% of collected samples contained Salmonella spp belonged to six serovars; Salmonella , enteritidis, Newport, derby, senftenberg and Virchow. These six serovars were checked by PCR for presence of three genes involved in virulence and toxin production, invA, avrA and stn. The gene invA was detected in all serovars, while avrA and stn genes were found in only 4 serovars. In this regard, S.typhimurium was found to harbour the three tested genes. When Salmonella typhimurium grew on normal synthetic medium and natural animal cells (Red blood; RBC and murine epithelial cells; IEC-6) and incubated separately at different temperatures 5, 25, 35 and 40 C for 60 h., they showed regular increase in growth rate with increasing temperature. Also, total RNA concentrations increased up to 24 h. then slightly decreased at each examined temperature specially at 25, 35 and 40 C, but the highest RNA concentration was observed at 40 C. indicating its preparedness in the form of metabolic and cellular activities to cope with temperature stress. Moreover, S. typhimurium seems to be more potent and showed increased ability to induce the expression of enterotoxin gene (stn) by the exposure of temperature elevation specially when grown on murine epithelial cells; IEC-6 comparing with synthetic media or red blood cells.