Efficacy of Individual Bacteriophages Does Not Predict Efficacy of Bacteriophage Cocktails for Control of Escherichia coli O157.

Yan D Niu,Hechao Du,Guihua Wang,Kim Stanford,Hui Liu,El Sayed Mahmoud,Tim A Mcallister,Ruiqiang Meng

doi:10.3389/fmicb.2021.616712

Abstract

Effectiveness of bacteriophages AKFV33 (Tequintavirus, T5) and AHP24 (Rogunavirus, T1), wV7 (Tequatrovirus, T4), and AHP24S (Vequintavirus, rV5), as well as 11 cocktails of combinations of the four phages, were evaluated in vitro for biocontrol of six common phage types of Escherichia coli O157 (human and bovine origins) at different multiplicities of infection (MOIs; 0.01–1,000), temperatures (37 or 22°C), and exposure times (10–22 h). Phage efficacy against O157 was highest at MOI 1,000 (P < 0.001) and after 14-18 h of exposure at 22°C (P < 0.001). The activity of individual phages against O157 did not predict the activity of a cocktail of these phages even at the same temperature and MOI. Combinations of phages were neutral (no better or worse than the most effective constituent phages acting alone), displayed facilitation (greater efficacy than the most effective constituent phages acting alone), or antagonistic (lower efficacy than the most effective constituent phages acting alone). Across MOIs, temperatures, exposure time, and O157 strains, a cocktail of T1, T4, and rV5 was most effective (P < 0.05) against O157, although T1 and rV5 were less effective (P < 0.001) than other individual phages. T5 was the most effective individual phages (P < 0.05), but was antagonistic to other phages, particularly rV5 and T4 + rV5. Interactions among phages were influenced by phage genera and phage combination, O157 strains, MOIs, incubation temperatures, and times. Based on this study, future development of phage cocktails should, as a minimum, include confirmation of a lack of antagonism among constituent phages and preferably confirmation of facilitation or synergistic effects.

Highlights

Bacteriophages are natural predators of bacteria, targeting specific bacterial species or strains
Across MOIs, phages, and O157 strains, anti-O157 efficacy of phages was 2.8 times [95% confidence interval (CI) 2.44-3.40, P < 0.001] more likely achieved between 14 and 18 h of incubation than at 22 h at 22◦C
Times, phages, and O157 strains, the likelihood of achieving superior efficacy at an MOI of 1,000 was >23 times higher than at an MOI of 0.01

Summary

Introduction

Bacteriophages (phages) are natural predators of bacteria, targeting specific bacterial species or strains. Bourdin et al (2014) found that a cocktail of three T4-like phages exhibited a narrower host range against Escherichia coli strains in broth culture as compared with when these phages were used individually. These previous studies indicate that combining phages into a cocktail may create phage antagonism, making the actual lytic activity less than the sum of its constituents

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