Synergistic effect of phage therapy using a cocktail rather than a single phage in the control of severe colibacillosis in quails.

Abstract

Infections associated with avian pathogenic Escherichia coli (APEC) cause severe economic losses to the poultry industry. The study presented herein investigated the in vivo performance of a single phage with prolonged in vivo and in vitro survivability alone or in combination with 3 other selected phages in treating colibacillosis in quails. Japanese quails (N = 360) were randomly assigned to 6 treatment groups with 4 replicate pens. Birds from the control groups (groups I, II, and III) were treated with 200μL sterile PBS (pH 7.4), 200μL of the selected phage (1010 pfu; TM3) or a cocktail of 4 phages (TM3 plus TM1, TM2, and TM4), respectively. Groups IV, V, and VI were challenged with 200μL E. coli (108 cfu; O78:K80 and O2:K1) and treated with i.m. injection of 200μL sterile PBS, phage TM3, or cocktail of 4 phages, respectively. Based on the results of the present study, the total mortality rate decreased from 46.6% in the untreated E. coli-challenged group to 26.5% and 13.6% in the E. coli-challenged group treated with single phage or phage cocktail, respectively. The body weights of birds treated with the phage cocktail were higher than the body weights of untreated birds on days 7, 14, and 21 post-challenge (P < 0.05). In addition, total viable cell counts of E. coli in the lungs of birds treated with the phage cocktail were lower than those of birds treated with phage TM3 on days 3 and 10 post-challenge (P < 0.05). Moreover, the incidence and severity of lesions in lungs, heart, and liver were found to be significantly less in the E. coli- challenged group treated with the phage cocktail. In conclusion, this study indicates that a phage cocktail may be more efficient in treating colibacillosis than a single phage possibly due to a synergistic effect between the individual phages.