Lytic bacteriophage for efficient biocontrol of Salmonella Typhimurium in foods

Food contamination with bacteria is a major problem worldwide, including Thailand. Presently, chemical food preservatives have been commonly used to solve this problem. However, their potential health risk has become a consumers’ concern. Therefore, many research efforts have been made to find safe antimicrobial agents to replace chemical food preservatives. Bacteriophages have received increase attention as safe biocontrol agents because the several bacteriophages have been approved by the United State Food and Drug Administration (USFDA) to be able to use in foods.
The objectives of this study were to isolate a bacteriophage specific to Salmonella Typimurium ATCC 13311 from water collected from a swine lagoon and to study some of its characteristics. Furthermore, its ability to control S.Typhimurium ATCC 13311 in beverages was also investigated. In this study, a lytic bacteriophage, specific to S.Typhimurium ATCC 13311, was isolated and designated as bacteriophage ST1. It had a broad host range inactivating not only S.Typhimurium ATCC 13311, but also Shigella dysemteriae (type1) DMST 2137 and Salmonella Typhi DMST 5784. The bacteriophage was stable at 50 and 60 C for 3 min and over a wide pH range (5 to 11). Approximately 80% of bacteriophage particles adsorbed to the host cells within 40 min after infection. One-step growth kinetics of the bacteriophage showed that the latent and burst periods were 70 and 330 min, respectively, and the burst size was about 172 PFU/infected cell. Its genome was double stranded DNA. Transmission electron microscopy revealed that the bacteriophage had an isometric head of about 70 nm in diameter and a long noncontractile tail of about 150 nm long and 7 nm wide.
It was classified as a member of the family Siphoviridae. For experiments in beverages, bacteriophage ST1 was stable in soy bean milk and jelly grass drink but not in guava juice and orange juice. When applied bacteriophage ST1 together with S. Typhimurium ATTC 13311 (106 CFU/ml) in soy bean milk and jelly grass drink, the bacteriophage reduced the bacterial cells with a dose dependent pattern. The application of more bacteriophage (108 PFU/ml) was more effective than lower doses (106 and 107 PFU/ml). This study suggests that bacteriophage ST1 has a potential for being use as a biocontrol agent against S.Typhimurium in beverages.