Isolation and characterization of a relatively broad-spectrum phage against Escherichia coli.

Multiple pathogenic types or serotypes restrict treatment for colibacillosis. In addition, rising antibiotic resistance has heightened public awareness to prevent and control pathogenic Escherichia coli. The bacteriophage is a viable technique to treat colibacillosis as an alternative to antibiotics. In this study, PH444, a relatively broad-spectrum obligate lytic phage, was screened from 48 Shiga toxin-producing Escherichia coli (STEC) phages isolated from farm manure samples and sewage samples in order to conduct genome-wide analysis, biological characterization, and a bacterial challenge experiment in milk. The results demonstrated that PH444 was a T7-like phage with a double-stranded DNA of 115,111 bp that belongs to the Kuravirus and was stable at temperatures between 4 and 50 °C and a pH range of 3 to 11. After adding PH444, the bacterial load in milk could be reduced from 3 × 103 PFU/ mL to zero within 1 h. In consideration of the biological properties of phage PH444, it was, therefore, demonstrated that PH444 has the potential to be used in phage biocontrol.

Characterization and genomic analysis of a Demerecviridae phage SP76 with lytic multiple-serotypes of Salmonella.

With the increase in antimicrobial resistance of Salmonella, phages have been paid more attention to as an alternative to antibiotics. In this study, a phage designated as SP76 was isolated from sewage. It can lyse several serotypes of Salmonella, including S. typhimurium (21/33), S. enteritidis (7/7), S. dublin (4/4), S. pullorum (2/2) and S. choleraesuis (1/2). SP76 showed a latent time of about 10 min, and maintained good lytic activity at a pH range of 3-10 and temperatures between 4 and 37 °C. Moreover, its optimal multiplicity of infection (MOI) was 0.0001. Based on the results of genomic sequence and analysis, SP76 was found to have a genome of 111,639 bp that encoded 166 predicted ORFs and belong to the Demerecviridae family, order Caudovirales. No virulence or lysogen formation gene clusters were identified in the SP76 genome. A pan-genome analysis based on 100 phages within the subfamily Markadamsvirinae indicated that SP76 had 23 core genes and 1199 accessory genes. We grouped the subfamily Markadamsvirinae and found that the main difference was in group III. In vitro bacteriostasis, experiments showed that the phage SP76 reduced planktonic bacteria by 1.52 log10 CFU/mL, and biofilms (24 h old) by 0.372 log10 CFU/mL, respectively. Thus, we isolated a safe and efficient phage that might be a good antibacterial agent.