Detecção, prevalência e expressão de genes de enterotoxinas clássicas de Staphylococcus aureus isolados de alimentos e surtos.

Abstract

Staphylococcus aureus (S. aureus) is among the bacteria of the genus Staphylococcus, species more related to cases and/or outbreaks of food poisoning, which are caused by staphylococcal enterotoxins (SE). These bacteria can be easily found in foods of animal origin. From the 22 SE described in the bibliography, approximately 95% of food poisoning outbreaks are associated to classic SE (SEA, SEB, SEC, SED and SEE). Thus, this study aimed at verifying the presence and the levels of expression of genes of classic SE in 13 S. aureus derived from different staphylococcal food poisoning outbreaks which took place in the state of Rio Grande do Sul (RS) and S. aureus isolated of chicken carcass in southern Brazil, by PCR and PCR real time (qPCR). Moreover, evaluated the effects of temperature (8° and 12°C) and saline concentration (2,5% NaCl) in the levels of transcriptional expression of genes of classic SE S. aureus through mRNA analysis. It has been observed that, with exception two isolated derived from outbreaks, the other shave shown transcriptional expression equal or bigger than standard strain for at least one of the genes of classic enterotoxins. Moreover, it has been observed that four isolated have expressed genes of one enterotoxin, while the others have shown expressions of at least two enterotoxins genes.Although there is no information related to which enterotoxin has caused the food poisoning in the evaluated outbreaks, the prevalence of classic SE, along with high levels of transcriptional expression showed that one or more classic SE caused of food poisoning outbreaks in which the isolated of S. aureus were obtained. Twelve isolated of S. aureus originated from chicken carcass carried the genes of these SE, being that in only five has been observed the transcriptional expression. In the five isolated there was expression of more of SE gene, demonstrating their potential toxigenic. These five isolates and standard strains were submitted to four treatments: 1) in ideal S .aureus multiplication; 2) in saline concentration of 2,5 of NaCI; 3) with incubation temperature of 12°C and; 4) with incubation in temperature of 8°C. The saline concentration and the low temperatures interfere in the expressions of genes of classic SE diminishing their values, nevertheless, even in saline concentration of 2,5 and in temperature of 12°C the isolated have expressed the genes of classic SE, demonstrating their toxigenic potential. Temperatures of 8°C have shown to be more efficient in the control of gene expression of S. aureus classic SE.