Effect of Environmental Factors on Expression of Staphylococcal Enterotoxins Genes

Abstract

Staphylococcal enterotoxins (SEs) secreted by S. aureus can cause foodborne disease, nausea, vomiting and diarrhea and even death. Regulation of SEs Expression is related to accessory gene regulators (Agr). It is important that revealing which environmental factors influencing on regulation of SEs expression to prevention of SEs food poisoning outbreak. Hence, natural environment factors which may be impact on SEs expression were selected, such as Temperature, food types, strains and competing strains. Seven strains of S. aureus carrying different SEs genes were collected from CAIQ strain bank for study. Strains were cultured with different conditions. Temperature, 8℃, 22℃, and 30℃. Food type, milk powder, and nutrient broth. Competing strains, V. parahaemolyticus, E. coli and B. cereus. The expression culture solution was pretreated by centrifugation, then determined by using SDS-PAGE, and distinguished SEs apart from each other by HPLC-ESI-TOF. There are 168 samples collected from SEs expression culture, the result of SDS-PAGE suggests 23 samples were positive for SEs, the other 145 samples were negative for SEs. The result of HPLC-ESI-TOF suggests that SEs with similar molecular weight can be distinguished by in term of m/z. The most important factor contributing to regulate expression of SEs was estimated by regressive analysis. The result shows that R2 was 0.14, F was 6.631 (p＜0.05), this result illustrates that at least one of the factors, strains, food types, temperature, and competing strains was responsible for SEs expression. The regression coefficients of four factors were -0.060 (p＜0.05), -0.074 (p＜0.05), 0.170 (p＜0.05) and 0.060 (p＞0.05). According to regression coefficients, competing strains is not significant influencing on SEs expression, and temperature is key factor for stimulating SEs expression, and had high expression at 30℃. Consequently, food easy contaminated with S. aureus should be monitored intensively at early and late summer, when proper temperature for expressing SEs may results in S. aureus food poisoning prevalence.