Biocontrol of Staphylococcus aureus in dairy products using lytic bacteriophage UHP46: efficacy in milk, cheese, and yogurt.

Staphylococcus aureus is a major public health concern in the dairy industry. It is a well-recognized pathogen responsible for bovine mastitis and raw milk contamination; certain strains produce heat-stable enterotoxin capable of causing staphylococcal food poisoning in humans. The emergence of multiple drug-resistant strains of S. aureus has rendered ineffective the use of antibiotics for control purposes. This study determined the antibacterial activity of lytic bacteriophage UHP46 against a single, previously characterized multidrug-resistant mastitis isolate, S. aureus S46, in three dairy matrices - milk, cheese and yogurt - under storage conditions representing refrigerated storage (4 °C), ambient conditions (25 °C) and a 37 °C mechanistic reference condition. UHP46 significantly reduced S. aureus S46 counts in milk, achieving reductions of 3.2 and 3.7 log₁₀ CFU/mL after 4 and 24 h at 4 °C, 2.1 and 3.1 log₁₀ CFU/mL after 4 and 24 h at 25 °C, and 1.8 log₁₀ CFU/mL after 3 h at 37 °C. The reduction at 37 °C was accompanied by an increase in phage titer from 7.2 to 8.8 log₁₀ PFU/mL. Application of UHP46 to cheese resulted in an immediate reduction of 0.6 log₁₀ CFU/g after 5 min of treatment at room temperature. The maximum reduction observed was 2.0 log₁₀ CFU/g at 24 h, with a sustained reduction of 1.9 log₁₀ CFU/g maintained through 96 h of refrigerated storage at 4 °C. In yogurt, net reductions on day 6 were 2.8, 2.7, and 1.6 log₁₀ CFU/g at 37 °C, 25 °C, and 4 °C, respectively. The findings indicate that UHP46 exhibits significant antibacterial activity against S. aureus S46 within the tested dairy matrices and under the evaluated storage conditions. However, as all challenge experiments utilized a single host strain, its efficacy against a broader panel of S. aureus, including methicillin-resistant S. aureus (MRSA), remains to be determined.