Isolation and characterization of lytic bacteriophages against enterohaemorrhagic Escherichia coli


Viazis, S., Akhtar, M., Feirtag, J., Brabban, A.D., Diez-Gonzalez, F. (2011). Isolation and characterization of lytic bacteriophages against enterohaemorrhagic Escherichia coli, 110(5), 1323-1331.

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Bacteriophages (bacteria eaters) are viruses capable of infecting and killing bacteria in a strain-specific manor. They are promising biocontrol and therapeutic tools for various bacterial pathogens and hence can be used to enhance food safety. Understanding the pathogenicity fitness of any growing bacteriophage resistant bacterial mutants is crucial when bacteriophages are assessed as an antimicrobial agent. Expression of selected pathogenicity genes in bacteriophage sensitive and resistant strains of two important foodborne pathogens, E. coli O157:H7 and Salmonella Newport, were investigated. The results of this study have shown that the developed bacteriophage resistant strains are behaving in a similar way to their parental bacteriophage sensitive strains. Although a more holistic approach is required, the findings of this study provide further support for the safe application of bacteriophages as biocontrol agents to enhance food safety.


Aims: The objective of this study was to isolate, identify and characterize a collection of lytic bacteriophages capable of infecting enterohaemorrhagic Escherichia coli (EHEC) serotypes. Methods and Results: Phages were isolated from dairy and cattle feedlot manure using E. coli O157, O26 and O111 strains as hosts. Phages were enriched from faecal slurries by culture in 10× trypticase soy broth at 37°C overnight. Phage plaques were obtained by mixing the filtered culture supernatant with molten tryptone agar containing the phage E. coli host strain, pouring the inoculated agar on top of cooled TS agar and incubating the culture overnight. Phages were purified from plaques and screened against additional E. coli and EHEC strains by the efficiency of plating method (EOP). Phage CEV2, and five other phages previously isolated, were able to lyse all of the 15 O157 strains tested with EOP values consistently above 0·001. Two phages were found to be highly effective against strains of E. coli O157 through EOP tests and against O26 strains through spot tests, but not against the O serogroup 111 strains. A cocktail of eight phage that lyse E. coli O157 strains resulted in >5logCFUml-1 reductions at 37°C. Multiplex-PCR revealed that none of these eight phages carried stx1, stx2, hlyA or eaeA genes. Conclusions: A cocktail of bacteriophages was capable of lysing most strains of two EHEC serotypes. Significance and Impact of the Study: This collection of phages can be combined and potentially used as an antimicrobial cocktail to inactivate E. coli strains from O serogroups 157 and 26 and reduce their incidence in the food chain. © 2011 The Authors. Journal of Applied Microbiology © 2011 The Society for Applied Microbiology.

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