Isolation and characterization of phage ISTP3 for bio-control application against drug-resistant Salmonella

Salmonella including drug-resistant strains are major foodborne pathogens causing serious illness and pose a great threat to the prevention and control for food safety. Phages can naturally defect the bacterium, is considered as a new and promising biological antimicrobial agent in the post-antibiotic era. A poultry facility in Wuhan, China provided wastewater samples from which a collection of 29 phages were isolated and purified. A broad host spectrum phage ISTP3, which capable of infecting all tested Salmonella, including drug-resistant Salmonella enterica, were examined. Additionally, the effectiveness of this phage ISTP3 in reducing drug-resistant S. enterica was assessed in diverse food samples. Transmission electron microscopy (TEM) and whole genome sequencing demonstrated that ISTP3 was found to belong to family Ackermannviridae. The one-step growth experiment and assays of stability demonstrated that ISTP3 exhibited short periods of inactivity before replicating, produced a significant number of viral progeny during infection, and remained high stable under varying pH and temperature conditions. We evaluated the efficacy of phage ISTP3 against drug-resistant Salmonella on chicken breast and lettuce samples at different temperatures. When applying phage ISTP3 in food matrices, the drug resistant Salmonella count significantly reduced at 4°C and 25°C at an MOI of 100 or 1,000 within a timescale of 12 h. Overall, the results, such as broad host ranges, strictly lytic lifestyles, absence of lysogenic related genes, toxin genes, or virulence genes in the genome, demonstrate that the application of phage ISTP3 as a biocontrol agent has promising potential for preventing and controlling drug-resistant S. typhimurium in the context of food safety, processing, and production

Application of a Phage Cocktail for Control of Salmonella in Foods and Reducing Biofilms

Salmonella contamination in foods and their formation of biofilms in food processing facility are the primary bacterial cause of a significant number of foodborne outbreaks and infections. Broad lytic phages are promising alternatives to conventional technologies for pathogen biocontrol in food matrices and reducing biofilms. In this study, 42 Salmonella phages were isolated from environmentally-sourced water samples. We characterized the host range and lytic capacity of phages LPSTLL, LPST94 and LPST153 against Salmonella spp., and all showed a wide host range and broad lytic activity. Electron microscopy analysis indicated that LPSTLL, LPST94, and LPST153 belonged to the family of Siphoviridae, Ackermannviridae and Podoviridae, respectively. We established a phage cocktail containing three phages (LPSTLL, LPST94 and LPST153) that had broad spectrum to lyse diverse Salmonella serovars. A significant decrease was observed in Salmonella with a viable count of 3 log10 CFU in milk and chicken breast at either 25 °C or 4 °C. It was found that treatment with phage cocktail was able to significantly reduced biofilm on a 96-well microplate (44–63%) and on a stainless steel surface (5.23 to 6.42 log10). These findings demonstrated that the phage cocktail described in this study can be potentially used as a biological control agent against Salmonella in food products and also has the effect to reduce Salmonella formed biofilms

Application of a broad range lytic phage LPST94 for biological control of salmonella in foods

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Salmonella, one of the most common food-borne pathogens, is a significant public health and economic burden worldwide. Lytic phages are viable alternatives to conventional technologies for pathogen biocontrol in food products. In this study, 40 Salmonella phages were isolated from environmentally sourced water samples. We characterized the lytic range against Salmonella and among all isolates, phage LPST94 showed the broadest lytic spectrum and the highest lytic activity. Electron microscopy and genome sequencing indicated that LPST94 belongs to the Ackermannviridae family. Further studies showed this phage is robust, tolerating a wide range of pH (4–12) and temperature (30–60◦C) over 60 min. The efficacy of phage LPST94 as a biological control agent was evaluated in various food products (milk, apple juice, chicken breast, and lettuce) inoculated with non-typhoidal Salmonella species at different temperatures. Interestingly, the anti-Salmonella efficacy of phage LPST94 was greater at 4◦C than 25◦C, although the efficacy varied between different food models. Adding phage LPST94 to Salmonella inoculated milk decreased the Salmonella count by 3 log10 CFU/mL at 4◦C and 0.84 to 2.56 log10 CFU/mL at 25◦C using an MOI of 1000 and 10000, respectively. In apple juice, chicken breast, and lettuce, the Salmonella count was decreased by 3 log10 CFU/mL at both 4◦C and 25◦C after applying phage LPST94 at an MOI of 1000 and 10,000, within a timescale of 48 h. The findings demonstrated that phage LPST94 is a promising candidate for biological control agents against pathogenic Salmonella and has the potential to be applied across different food matrices

Characterization of Salmonella Phage LPST153 That Effectively Targets Most Prevalent Salmonella Serovars

Foodborne diseases represent a major risk to public health worldwide. In this study, LPST153, a novel Salmonella lytic phage with halo (indicative of potential depolymerase activity) was isolated by employing Salmonella enterica serovar Typhimurium ATCC 13311 as the host and had excellent lytic potential against Salmonella. LPST153 is effectively able to lyse most prevalent tested serotypes of Salmonella, including S. Typhimurium, S. Enteritidis, S. Pullorum and S. Gallinarum. Morphological analysis revealed that phage LPST153 belongs to Podoviridae family and Caudovirales order and could completely prevent host bacterial growth within 9 h at multiplicity of infection (MOI) of 0.1, 1, 10 and 100. LPST153 had a latent period of 10 min and a burst size of 113 ± 8 PFU/cell. Characterization of the phage LPST153 revealed that it would be active and stable in some harsh environments or in different conditions of food processing and storage. After genome sequencing and phylogenetic analysis, it is confirmed that LPST153 is a new member of the Teseptimavirus genus of Autographivirinae subfamily. Further application experiments showed that this phage has potential in controlling Salmonella in milk and sausage. LPST153 was also able to inhibit the formation of biofilms and it had the ability to reduce and kill bacteria from inside, including existing biofilms. Therefore, the phage LPST153 could be used as a potential antibacterial agent for Salmonella control in the food industry