Characterization of enterohaemorrhagic Escherichia coli O157:H7 phages FEC14 and FEC19 and their potential use in contaminated beef

Abstract:

[Background] Escherichia coli O157:H7 is one of the most important foodborne pathogens. The accelerated drug resistance of E. coli O157:H7 invokes the selection of phages with strong lytic properties to achieve the purpose of disease prevention and treatment with broad application prospects. [Objective] To isolate and identify lytic phages against E. coli O157:H7 and analyze their biological characteristics and bacteria-killing efficiency, which may provide insights into the research and application of phages. [Methods] Phages were isolated and purified using double-layer plate method, and their morphology was observed by transmission electron microscope (TEM). The optimal multiplicity of infection (MOI), one-step growth curve, pH and temperature stability were determined, and the whole genome of phages was sequenced. Lysis efficiency was determined by a single phage or cocktail method in contaminated beef. [Results] Two strains of lytic E. coli O157:H7 phages FEC14 and FEC19 were isolated and purified. According to TEM results, the heads of the two phages were both icosahedral, and FEC14 presented a head diameter of about 80 nm and star-shaped tail filaments, while FEC19 had a head diameter of about 58 nm and needle-shaped tail filaments. Moreover, FEC14 showed an optimal MOI of 0.001, the latent period of 15 min and the lysis period of 65 min with an average burst size of 156 PFU/cell, and FEC19 displayed an optimal MOI of 0.1, the latent period of 10 min and the lysis period of 80 min with an average burst size of 800 PFU/cell. FEC14 stabilized at 60 ℃ and pH 4.0–11.0, while FEC19 survived at 70 ℃ and pH 5.0–9.0. FEC14 belongs to the genus Kuttervirus, family Ackermannviridae, order Caudovirales, and FEC19 falls into the genus Wifcevirus, family Myoviridae, and order Caudovirales. The single phage or phage cocktail effectively inhibited the growth of host bacteria in the contaminated beef, and the two phages had no known virulence genes and drug resistance genes, showing great potential efficacy in the control of E. coli O157:H7 contamination. [Conclusion] Two strains of lytic E. coli O157:H7 phages FEC14 and FEC19 with high specificity, stability and lysis efficiency reveal their potential to be an alternative antimicrobial agent for food safety in the future.

Key words:Escherichia coli O157;bacteriophage;biological control;cocktail method