Isolation and identification of phages of food-borne pathogenic Escherichia coli O157:H7 and O55:H7

Abstract:

[Background] Enterohemorrhagic Escherichia coli (EHEC) O157:H7 and enteropathogenic E. coli (EPEC) O55:H7 are common food-borne pathogens, causing intestinal infection and other diseases. The specific bacteriophages are of great potential for the development of new antibacterial agents. [Objective] To isolate the phages of O157:H7 and O55:H7 and to characterize their biological and genomic characteristics for future development of phage therapy. [Methods] Phages were separated from environmental water samples by the double agar overlay plaque assay. Their biological characteristics, including morphology, multiplicity of infection (MOI), host range, as well as one-step growth curve, were studied. Their genomes were sequenced by the Illumina MiSeq and then analyzed with RAST, Prokka, BLASTp. [Results] We isolated two potent phages of Myoviridae family, vB_EcoM_P251 and vB_EcoM_P255, using E. coli O157:H7 and O55:H7 as host, respectively. Their optimal MOI were both 1, and 91.9% and 90.8% of them adsorbed to the respective host within 15 min. Their lysis activity was high and stable at 37–60 ℃ and pH 4.0–11.0. P251 was only infectious to E. coli O157:H7 and O78:H11, while P255 was infectious to 11 EHEC and EPEC strains, including O55:H7 and O157:H7. The P251 genome and P255 genome are 136 254 bp and 111 068 bp in length separately, with GC content of 37% and 35%, respectively. Their genomes contain 227 and 173 open reading frames (ORFs), separately, 80 and 73 of which share significant similarities to functional genes. Besides, P251 contains 2 tRNAs. In addition, genomes of P251 and P255 share 72.24% nucleotide identity over 48% of their length. [Conclusion] Two new O157:H7 and O55:H7 phages, P251 and P255, with strong lysis activity, wide host range, as well as a great application potential in food-borne pathogenic E. coli control, were isolated and identified.