Evaluation of phage-based treatments for combating Staphylococcus aureus biofilms on dairy surfaces

The ability of Staphylococcus aureus to establish strong biofilms in milk poses a significant threat to the consumer’s health and a challenge for the dairy industry. Here, we have evaluated the efficacy of phage-based treatments (phage Kayvirus rodi and lytic protein LysRODI∆Ami) for combating biofilm formation on polystyrene and stainless steel surfaces submerged in UHT skim milk compared to growth medium. An adaptive transcriptional response was observed in cells intended to metabolize lactose and to increase biofilm formation. Also, biofilms grown in milk exhibited a denser and more complex matrix, mainly composed of proteins, presumably casein. These changes in matrix composition and structure offered a high resistance to both LysRODI∆Ami (4 µM) and phage Kayvirus rodi (108 PFU/ml) individual treatments, although combination of the two led to some reduction in the number of attached cells. Both antimicrobials were more successful at biofilm inhibition, exhibiting a synergistic interaction when used together. Unexpectedly, the bacteriophage treatment exhibited enhanced efficacy to prevent biofilm development in milk compared to fresh medium. The shift in matrix composition and pH modulation might be behind these differences. This research contributes to the development of innovative strategies for ensuring milk quality and safety. Moreover, our results demonstrate the importance of testing antimicrobials under conditions that reflect the real-life application as much as possible. 6 samples were analyzed, correponding to 3 biological replicates of 24 hours biofilms formed by S. aureus 15981 in MILK ºC or TSBg