Survival of RB51 and S19 Vaccine Strains in Fresh and Ripened Cheeses.

Brucellosis is a zoonotic infection caused by the consumption of contaminated raw milk and dairy products. This study aims to compare survival rates of RB51 and S19 vaccine strains to that of virulent 2308 strain during the manufacture of fresh and ripened cheeses. To do this, we inoculated fresh pasteurized milk with RB51, S19, or 2308 at a 6 × 10 colony-forming unit per milliliter concentration during the cheese making process. Cheese was manufactured at room temperature, then, fresh cheeses were conserved at either 4°C or 25°C for 7 days, while ripened cheeses were conserved for 31 days at the same temperatures. We measured survival and pH values during different stages of the process. Our results confirm that all three strains can maintain viable cells in both types of cheeses throughout the process. Survival of RB51 was 10 times lower than was the survival of the S19 and 2308 strains in both fresh and ripened cheeses. Our results also suggest that both temperature and pH can condition survival. In conclusion, RB51 and S19 vaccine strains can survive throughout the manufacture and conservation processes of both fresh and ripened cheeses. In turn, this implies a potential health risk if cheeses contaminated with these strains were to be consumed.