Coliphage cocktails for controlling antimicrobial-resistantEscherichia coli: emphasizing polyphage and multihost interactions at different levels of multiplicity of infection

Abstract

Aim This study elucidates the in vitro bactericidal effectiveness of poly-phage cocktail combinations of 2, 4, 6, 8 and 10 individual coliphages against a cocktail of 20 AMR E. coli. Methods & results Different polyphage cocktails viz., 45 two-phage combinations, 28 four-phage combinations, 15 six-phage combinations, 6 eight-phage combinations and one ten-phage combination were formulated using a pool of ten coliphages that were isolated from two different geographical locations (East and West coasts of India). The different poly phage cocktails were tested at four different levels of Multiplicity of Infection (MOI) viz., MOI-1, MOI-10, MOI-100 and MOI-1000. All the 2, 4, 6, 8 and 10 phage cocktails were found to be effective in controlling the growth of a cocktail of 20 AMR bacteria when tested at MOI-1000 and MOI-100 but variations in antibacterial activity were observed at lower MOIs of 10 and 1. The ten coliphage cocktail showed lytic activity against 100% of AMR E. coli from farmed brackish water shrimp, 96% of laboratory collection of AMR E. coli, 92% of AMR E. coli from farmed freshwater fish and 85% of AMR E. coli from market shrimp. Conclusion Polyphage cocktails of 2, 4, 6, 8 and 10 coliphages applied at an MOI of 1000 effectively suppressed the growth of antimicrobial resistant E. coli. The results indicated phage-phage synergy in the lytic activity of several coliphage combinations at higher MOIs of 1000 and 100 while phage-phage antagonism was evidenced at lower MOIs of 10 and 1.