Posted: October 25th, 2011 - 2:15pm
Source: Applied and Environmental Microbiology

Salmonella enterica and Escherichia coli O157:H7 are major foodborne pathogens causing serious illness. Phage SFP10 was isolated and characterized, which revealed effective infection of both S. enterica and E. coli O157:H7. SFP10 contains a 158-kb double-stranded DNA genome belonging to the Vi01-like Myoviridae family. In vitro adsorption assays showed that the adsorption constant rates to both S. Typhimurium and E. coli O157:H7 were 2.50 x 10–8 ml/min and 1.91 x 10–8 ml/min, respectively. One-step growth analysis revealed that SFP10 has a shorter latent period (15 min) and larger burst size (>200 PFU) than ordinary Myoviridae phages, suggesting effective host infection and lytic activity. However, differential development of resistance to SFP10 in S. Typhimurium and E. coli O157:H7 was observed; bacteriophage-insensitive mutant (BIM) frequencies of 1.19 x 10–2 CFU/ml for S. Typhimurium and 4.58 x 10–5 CFU/ml for E. coli O157:H7 were found, indicating that SFP10 should be active and stable for control of E. coli O157:H7 with minimal emergence of SFP10-resistant pathogens, but may not for S. Typhimurium. Specific mutation of rfaL in S. Typhimurium and E. coli O157:H7 revealed the O-antigen as a SFP10 receptor for both bacteria. Genome sequence analysis of SFP10 and its comparative analysis with homologous Salmonella Vi01 and Shigella phiSboM-AG3 phages revealed that their tail fiber and tailspike genes share low sequence identity, implying that these genes are major host-specificity determinants. This is the first report identifying specific infection and inhibition of Salmonella Typhimurium and E. coli O157:H7 by a single bacteriophage.