Presence of sopE gene & its phenotypic expression among different serovars of Salmonella isolated from man & animals.

BACKGROUND & OBJECTIVES: Salmonellae cause a spectrum of diseases in man and animals but their virulence factors responsible for induction of gastroenteritis and/or systematic infection are still poorly understood. Also, the different subspecies and serovars of Salmonella differ considerably in their virulence for man and animals. There is increasing evidence that Salmonella possesses a dedicated protein secretion system denoted type III secretion system (TTSS) that is involved in the early stage of Salmonella infection. One such TTSS is Salmonella outer protein E (SopE) that helps in the invasion of Salmonella by stimulating membrane ruffling. In the present study the presence of sopE gene and its phenotypic expression (SopE protein) among different serovars of Salmonella enterica isolated from man and animals in India was investigated. METHODS: A total of 50 isolates of S. enterica belonging to 11 serovars were tested for the presence of sopE gene by polymerase chain reaction. The in vitro phenotypic expression of SopE protein was detected by Western blotting using anti-SopE serum. RESULTS: Of the 50 isolates of S. enterica belonging to 11 serovars tested for the presence of sopE,14 belonging to three serovars viz., Enteritidis, Gallinarum and Virchow were found to carry the sopE gene. Similarly, 13 isolates belonging to same three serovars were found to express SopE protein phenotypically as detected by Western blotting using anti-SopE serum. INTERPRETATION & CONCLUSION: The results indicated that sopE gene appeared to be distributed and conserved among only a few serovars of Salmonella (Enteritidis, Gallinarum and Virchow) irrespective of their source of isolation. The presence of sopE gene in Salmonella provides an important pathogenic means to invade epithelial cells.

Effect of norepinephrine on growth of Salmonella and its enterotoxin production.

Salmonella typhimurium was cultured in presence or absence of norepinephrine in conditioned media. Two conditioned media containing bovine and pig serum were prepared. Supplementation of fresh cultures with norepinephrine (5 x 10(-5) M per mL of medium) resulted in ten-fold increase in growth as compared to controls. No significant difference in growth of organisms in media containing bovine and pig serum was observed. Growth was more in culture incubated under shaking condition than in non-shaking condition. Enterotoxin production increased by two to eight-folds in the medium supplemented with norepinephrine.

Occurrence of sef & pef genes among different serovars of Salmonella.

A total of 29 strains of Salmonella enterica belonging to seven serovars isolated from human, animals and birds were used to study the occurrence of Salmonella fimbriae genes (sef and pef) by PCR amplification technique using their specific primers. All the strains (15) of S. Enteritidis were found to carry both sef and pef genes irrespective of the source of isolation. S. Typhimurium strains were found to harbour only pef genes, while S. Gallinarum strains harboured only sef genes. Other serovars namely, S. Newport, S. Kentucky, S. Weltevreden and S. Indiana were negative for both pef and sef genes. The importance of fimbriae in the pathogenesis of salmonellosis is suggested.

Induction of Salmonella enterotoxin (stn) gene expression by epithelial cells (IEC-6).

Prevalence of Salmonella enterotoxin (stn) gene among Salmonella enterica and S. bongori was investigated by polymerase chain reaction (PCR) and gene probe and its status of phenotypic expression was examined on chinese hamster ovary cells by cultivating the strains with conventional method for enterotoxin production and by cultivating the organisms in contact with intestinal epithelial cells of rats (IEC-6). All the 19 strains and serovars of S. enterica such as Typhimurium, Enteritidis, Newport, Weltevreden, Indiana, Gallinarum and Kentucky were found to carry stn gene as examined by PCR and gene probe but only a limited number of strains (13 out of 19) expressed phenotypically the enterotoxin when cultured by conventional method. Cultivation of organisms in contact with epithelial cells induced expression of stn gene phenotypically in all the 19 strains. In contrast to S. enterica, strains of S. bongori were found neither genotypically (stn) nor phenotypically (Stn) positive.