Short-tailed Salmonella Phage SWJM-03: Isolation, Characterization, and Application in Controlling Contamination on Lettuce

Salmonella enterica, a major cause of foodborne outbreaks associated with ready-to-eat leafy greens, like lettuce, poses urgent challenges to food safety. In this study, a lytic phage, SWJM-03, was isolated and evaluated for its potential as a biocontrol agent against Salmonella contamination in lettuce.

Phage SWJM-03 was isolated from sewage using multidrug-resistant Salmonella Typhimurium 2112 as the host, and its biological characteristics, genomic features, antibiofilm activity, and biocontrol efficacy on lettuce were evaluated. Phage SWJM-03 is classified within the genus Berlinvirus, class Caudoviricetes. The phage exhibited a short-tailed morphology and demonstrated rapid adsorption (92.7% within 20 min), a short latent period of 5 min, and a burst size of 97 PFU/cell. SWJM-03 showed high stability across a wide pH range (3-12) and retained high activity within a temperature range of 30-60°C relevant to food processing conditions. Notably, SWJM-03 also exhibited great storage stability, with minimal titer reduction after 4 weeks at 4°C, supporting its practical applicability. Genomic analysis (39 474 bp dsDNA, 48.97% G + C, GenBank Accession no.: OQ818670) confirmed the absence of virulence-associated genes. SWJM-03 significantly reduced biofilm biomass of S. Typhimurium by 56.8%, and demonstrated promising biocontrol potential. Importantly, in a simulated lettuce contamination system under refrigeration (4°C), SWJM-03 achieved up to 4.00 log₁₀ CFU/cm² reduction within 3 days, reducing bacterial counts below detectable levels (<10 CFU/cm²).

Phage SWJM-03 is a rapid-acting and environmentally stable lytic bacteriophage with strong antibacterial activity under refrigeration conditions, highlighting its potential as a promising biocontrol agent for controlling Salmonella contamination in fresh produce.