Isolation, characterization, and application of a lytic bacteriophage SSP49 to control Staphylococcus aureus contamination on baby spinach leaves.

Staphylococcus aureus, a major foodborne pathogen, is frequently detected in fresh produce. It often causes food poisoning accompanied by abdominal pain, diarrhea, and vomiting. Additionally, the abuse of antibiotics to control S. aureus has resulted in the emergence of antibiotics-resistant bacteria, such as methicillin resistant S. aureus. Therefore, bacteriophage, a natural antimicrobial agent, has been suggested as an alternative to antibiotics. In this study, a lytic phage SSP49 that specifically infects S. aureus was isolated from a sewage sample, and its morphological, biological, and genetic characteristics were determined. We found that phage SSP49 belongs to the Straboviridae family (Caudoviricetes class) and maintained host growth inhibition for 30 h in vitro. In addition, it showed high host specificity and a broad host range against various S. aureus strains. Receptor analysis revealed that phage SSP49 utilized cell wall teichoic acid as a host receptor. Whole genome sequencing revealed that the genome size of SSP49 was 137,283 bp and it contained 191 open reading frames. The genome of phage SSP49 did not contain genes related to lysogen formation, bacterial toxicity, and antibiotic resistance, suggesting its safety in food application. The activity of phage SSP49 was considerably stable under various high temperature and pH conditions. Furthermore, phage SSP49 effectively inhibited S. aureus growth on baby spinach leaves both at 4 °C and 25 °C while maintaining the numbers of active phage during treatments (reductions of 1.2 and 2.1 log CFU/cm, respectively). Thus, this study demonstrated the potential of phage SSP49 as an alternative natural biocontrol agent against S. aureus contamination in fresh produce.