Molecular typing of Staphylococcus aureus isolated from food samples in Iran

Staphylococcus aureus is the third most common cause of confirmed food poisoning in the world and is the predominant species involved in staphylococcal food poisoning outbreaks. Considerable genetic heterogeneity has been shown in natural populations of S. aureus isolates. Coagulase gene typing is one of the numerous molecular techniques to identify and compare S. aureus genotypes. The present study was conducted to type the coagulase gene in 25 S. aureus isolates isolated from food samples. All isolates were identified by routine biochemical tests and then confirmed by species-specific PCR and yielded products with the expected molecular size of 1.3 kb. PCR amplification of DNA with the primers COAG2 and COAG3 yielded single-banded PCR products in 24 isolates with the molecular size of approximately 500 bp (n = 2, 8 %), 750 bp (n = 1, 4 %), 850 bp (n = 12, 48 %), and 950 bp (n = 9, 36 %), while one isolate produced no band in PCR amplification of coagulase gene. Since human and bovine reservoirs of S. aureus represent two subpopulations that rarely cross-infect, detection of single bands by coagulase PCR in S. aureus isolates suggests that these isolates may be of bovine origin not human one, and contamination of food samples may initiate from the animal source not the food handlers. Digestion of coagulase PCR products with restriction endonuclease enzymes AluI and Hin6I yielded four different restriction profiles that indicate presence of heterogeneity in the coagulase gene of the isolates. This work showed that restriction analysis of the coagulase gene can be considered as a reliable and fast method for determining the origin of S. aureus in food samples. © 2013, Springer-Verlag London.