Detection of Staphylococcus aureus enterotoxin type I using qPCR

Abstract

Epidemiological surveillance reports revealed that Staphylococcus aureus ranked third among top bacterial pathogens causing food poisoning in Thailand during 2010-2012. Thailand Food and Drug Administration (FDA) abides by the international "zero tolerance" policy for staphylococcal enterotoxins (SEs). Specifically, SEs must be absent in 25 g of food, while the bacteria are tolerated at low level depending on the types of food. Increasing numbers of S. aureus isolates from foods carried the newly described staphylococcal enterotoxin type I (SEI) and type G (SEG) rather than the classic types (e.g., SEA and SEB) previously identified as the common cause of staphylococcal food poisoning. In this study, we developed a quantitative PCR (qPCR) for detection of SEI-encoding gene as SEI is the most prevalent enterotoxin in newly described SE subgroup 3 and is increasingly found in S. aureus isolates from food samples causing food poisoning. The designed sei primer and probe set is specific to S. aureus sei gene and can detect as low as 150 femtogram of the target (approximately 50 bacterial cells/ml of milk). We proposed that our sei primer and probe set can be used in multiplex qPCR assay along with the already developed primer and probe sets targeting classic sea and seb genes for enterotoxin detection in food safety surveillance.