Abstract

Milk and dairy products such as Cotija cheese are susceptible to contamination by Staphylococcus aureus. Some isolates of these bacteria carry the genes for enterotoxins and also the toxic shock syndrome toxin (TSST-1), additionally, many of these strains are potentially resistant to antibiotics. In the present study, a total of 50 samples of Cotija cheese sold at the Central Market "Baltazar R Leyva Mancilla” in the State of Guerrero were collected to determine the amount of bacteria growing in the cheese (expressed as CFU/g of cheese), the biotype, the antibiotype and the genotype. The results show that the amount of bacteria varies from 12x10³ to 3x10⁶CFU/g exceeding the permitted limits for ripened cheeses. Three biotypes were identified, 100% were susceptible to oxacylin, vancomycin, ciprofloxacin, trimethoprim-methoxazole, amikacin and clindamycin but tetracycline resistant. Only one of the four identified genotypes was positive to the TSST-1 gene. This is the first report of S. aureus isolated from Cotija cheese in the state of Guerrero, Mexico. Finally, our data evidenced cotija cheese as a vehicle carrying a large number of pathogenic S. aureus strains, suggesting that the public policy on food safety must be firmly reviewed.

Key words: Staphylococcus aureus, biotype, antibiotype, genotype, tsst-1, cheese.