Exploration of Bacteriophages Against Vancomycin-Resistant Enterococcus faecium : A Report from India

The vancomycin-resistant Enterococcus faecium (VREfm) has been declared as a high priority pathogen by World Health Organisation (WHO). It presents a major therapeutic challenge to healthcare, remaining with limited antibiotic options. Bacteriophage therapy has emerged as a promising alternative for combating antimicrobial-resistant pathogens. This study reports the isolation and characterization of bacteriophages active against VREfm and MDR E. faecium clinical isolates from India. Two bacteriophages, NIMS_EF375_N69_P9 (Φ1) and NIMS_EF375_N74_P12 (Φ2), were isolated from sewage by enrichment using MDR E. faecium strain EF375 as the propagation host. Lytic activity was confirmed by spot assay and double-layer soft agar plaque assay; both phages produced clear plaques of 1.5-2.0 mm. Transmission electron microscopy showed icosahedral heads with long non-contractile tails, presenting siphovirus-like morphotype within the class Caudoviricetes . Host range was assessed against 10 MDR E. faecium isolates (including the propagation host), 2 of which were VREfm. Φ1 lysed 5 of 10 isolates, including the VanA-type VREfm, whereas Φ2 lysed 7 of 10, including both VanA- and VanB-type VREfm. In time-kill assays against EF375 at an MOI of 1, Φ1 produced effective decline in optical density sustained through 24 h (∼80% reduction relative to the untreated control), whereas Φ2 suppressed bacterial growth with only ∼50% reduction. To the best of our knowledge, this study represents the first report from India on the isolation and characterization of bacteriophages active against clinical VREfm isolates. The broader host range of Φ2 and the stronger killing kinetics of Φ1 suggest complementary roles in a phage cocktail, warranting genomic characterization and in vivo evaluation.