The efficacy of a bacteriophage against food-derived Salmonella Typhimurium isolates

Background and Aim : Salmonellosis is of major foodborne bacterial gastroenteritis and an important zoonosis worldwide. Nontyphoidal salmonellae are estimated to cause approximately ۱۵۳ million cases of gastroenteritis and ۵۷,۰۰۰ deaths globally each year. Bacteriophages are viruses that specifically kill bacteria. Phage-based biocontrol is a natural approach to combat food-borne bacteria at different stages of the food production chain. This study aimed to isolate and characterize novel bacteriophages as a potential candidate for biocontrol of Salmonella Typhimurium in food. Methods : Fifty-two samples collected from different poultry and cattle farms in northern Germany. Soft-agar overlay technique was applied for isolating Salmonella-specific phages by using S. Typhimurium LT۲. Host range determination was conducted using ۱۶ food-originated Salmonella isolates, two E. coli O۱۵۷:H۷, and S. LT۲. Three hosts were selected for further investigations. For one-step growth analysis, SP۱ was incubated at ۳۷ °C with the three hosts. Phage concentration was measured at ۵ or ۱۰ min-intervals for ۲ h. The inhibitory effect of SP۱ at different titers was tested in liquid medium at ۳۷ °C. The absorbance at ۵۹۵ nm was measured every ۱۰ min for ۱۰ h. The phage inhibitory effect was also tested at ۴ °C, at MOIs of ۱۰۴ and ۱۰۵. Results : Nine bacteriophages were isolated from chicken fecal samples. One bacteriophage was isolated from a nasal swab of a cow. Based on the stability and growth of the isolated phages, four bacteriophages were selected for host range determination. Among the isolated phages, SP۱ demonstrated broader host range and strong lytic effects on S. LT۲ and three food-derived Salmonella Typhimurium isolates. S. LT۲, S۱ and S۲ were selected as the most susceptible hosts for further investigations. One-step growth curve analysis of the phage demonstrated a ۶۰-min latent period and a burst size of ۵۰-۶۱ PFU/infected cell in the three hosts. Phage-host interaction investigations in liquid medium showed that SP۱ can suppress the growth of Salmonella isolates at ۳۷ °C for ten hours. At ۴ °C, a reduction of ۱.۴ to ۳ log units was observed in the three hosts. Conclusion : SP۱ phage can be a promising candidate for biocontrol of Salmonella Typhimurium in food.

کلیدواژه ها:

Salmonella Typhimurium ، bacteriophages ، biocontrol ، antimicrobial