Development and evaluation of technology for preserving hard cheese with staphylococcal bacteriophage

Despite the control of dairy products by microbiological indicators, this category of products is among those that most often cause alimentary infections and poisonings among consumers. At the same time, the most dangerous food pathogens are Campylobacter, Salmonella, Listeria monocytogenes and toxin-producing pathogens ‒ Staphylococcus aureus. Therefore, the issue of increasing the microbiological safety of dairy products, including hard cheese, is constantly relevant. This search aimed to determine S. aureus contamination of raw milk and hard cheeses and assess the influence of isolated bacteriophages on the development of staphylococci and lactic acid microorganisms during cheese ripening. S. aureus was not detected in 25.5% of raw milk samples received for processing. In comparison, the bulk of the milk – 52.9% of the samples – was contaminated with coagulase-positive staphylococci up to 500 CFU/ml. 21.6% of raw milk samples at the processing plant contained S. aureus more than 500 CFU/ml. Hard cheeses sold in the trade network did not contain S.aureus in 70.4% of samples; in 22.2%, its amount did not exceed 5 ×102 CFU/g, and in 7.4% of cheese samples, the content of S.aureus was higher than the standard norm of 5 ×102 CFU/g. From 30.4 to 60.8% of raw milk samples contained virulent phages that lysed S. aureus, which was isolated from hard cheeses and dairy raw materials. Two phages (No. 4 and No. 8) were isolated from raw milk, which showed 80.0 – 90.0% virulent activity in four crosses against both S. aureus isolated from milk and rennet cheeses. These phages were introduced into the technology of hard cheese production. The addition of virulent staphylococcal bacteriophages to the milk mixture (2 ml per 1 l at a concentration of 108 CFU/ml) during the production technology of hard cheese allows its preservation against the development of S. aureus. Thus, a technology for the biocontrol of S. aureus in hard cheese has been developed, almost wholly neutralizing it during production.