Characterization of a bacteriophage, isolated from chicken farms, that is lytic against mcr-positive Escherichia coli strains

Abstract

The occurrence and prevalence of mcr gene in Gram-negative bacteria from animals was firstly reported in 2015, which greatly threat the values of the human last-resort antimicrobial-colistin. Here we have isolated a lytic bacteriophage, designated vB_EcoM_mcr1, from sewage effluent of a chicken farm in Jiangsu, Mid-east of China, which could infect mcr-positive Escherichia coli strains. Electron microscopy showed Phage vB_EcoM_mcr1 does not resemble to any known family of the phage, with an isometric head (110 nm) and a short contractile tail (35 nm). The phage showed a narrow host ranges against E. coli isolates of chicken origin, lysing 3 of 34 (8.8%) mcr-positive strains. Its latent period and burst size were approximately 5 min and 34 PFU/cell, respectively. The genome of phage vB_KpnM_mcr1 was double stranded DNA and estimated to be about 60 kb. The bacteriolytic activity of this phage at a multiplicity infection (MOI) of ≥0.001 indicted its efficiency for reducing bacterial growth. It is the first time to identify the phage, vB_EcoM_mcr1,which could infect mcr-positive E. coli. These findings suggest that phage vB_EcoM_mcr1 could be considered as a potential therapeutic or prophylactic candidate against mcr-positive E. coli infection in chicken.