Characterization and Infection Receptor Analysis of Bacteriophages for Escherichia coli O157:H7 and non-O157 Shiga Toxin-Producing E. coli

Introduction: Shiga Toxin-producing Escherichia coli (STEC) are one of the pathogenic E. coli and produce Shiga Toxins. Although E. coli O157:H7 has been involved in most of outbreaks in the world, non-O157 STEC serotypes are also associated with outbreaks and severe human illness.

Purpose: The objective of this study was to isolate bacteriophages for E. coli O157:H7 and non-O157 STEC and compare physiological characteristics. Also, infection receptor analysis of bacteriophages for E. coli O157:H7 and non-O157 STEC, which might be associated with phage-host recognition, was conducted.

Methods: Seven bacteriophages for E. coli O157:H7 and non-O157 STEC were isolated from various environmental samples, respectively, and characterized using plaque assay. Also, random mutant library was constructed by transposon mutagenesis, and phage resistant mutants were screened for bacteriophage receptor identification.

Results: As the result, E. coli O157:H7 bacteriophages, which belonged to Siphoviridae family, were specific only to 24 E. coli O157:H7 strains with 95% infection rate, while non-O157 STEC bacteriophages, which belonged to Myoviridae family, showed broad host range in 10 non-O157 STEC strains, 24 E. coli O157:H7 strains and 51 non-pathogenic E. coli strains. In stability test, only 22% and 11% of E. coli O157:H7 bacteriophages averagely decreased under pH 3 and 70% ethanol for an hour, respectively, while 48% and 56% of non-O157 STEC bacteriophages averagely decreased under the same conditions, respectively. In infection receptor analysis, E. coli O157:H7 bacteriophages recognized O-antigen as a receptor when they infected E. coli O157:H7 ATCC 43890, and non-O157 STEC bacteriophages recognized core as a receptor when they infected E. coli O103 NCCP 13937.

Significance: In conclusion, E. coli O157:H7 and non-O157 STEC bacteriophages might have different morphological characteristics and host spectrum, and E. coli O157:H7 bacteriophages might be more stable than non-O157 STEC bacteriophages under harsh conditions of acidic pH and organic solvent. Also, each receptor of two bacteriophage groups could result from different part of lipopolysaccharide.