Isolation and characterization of two lytic phages against multidrug-resistant Salmonella and their application as a cocktail for biocontrol in foods

Currently, multidrug-resistant Salmonella contamination prevention and control are facing with enormous difficulties and challenges in food contamination management. In this study, two lytic Salmonella phages (SWJM-01 and SWJM-02), belonged to Kuttervirus and Felixounavirus family, respectively, were isolated and characterized. The dsDNA genome sequence of SWJM-01 was 155,472 bp with 44.91% GC content, encoding 206 open reading frames (ORFs), while SWJM-02 was 84,679 bp with 38.98% GC content, encoding 147 ORFs. The latent periods of SWJM-01 and SWJM-02 were both 20 min. Their burst sizes were about 52 and 108 FPU/infected cell, respectively. SWJM-01 and SWJM-02 can lytic19.1% and 95.2% of Salmonella (total 42 strains), respectively, revealing that SWJM-02 is bacteriophage with wide spectrum. In addition, they both maintained relatively high activities in broad environment conditions of pH (4-12) and temperature (30-60 degrees C). Furthermore, the OD600 values after treatment with SWJM-01, SWJM-02 and their cocktail declined to 1.037, 0.762 and 0.341, respectively, as well as the bacterial counts in lettuce and milk significantly reduced after treatment with phages and their cocktail at 4 degrees C for 3 d. All results suggested that these two phages can be used as antibacterial agents to control Salmonella contamination in foods, especially phage cocktail.