Isolation and characterisation of a novel Stenotrophomonas maltophilia phage vB_SmaS_BCU-1 with evaluation of mammalian cell safety

Stenotrophomonas maltophilia (S. maltophilia), is a low virulence opportunistic pathogen intrinsically resistant to a wide range of antibiotics with several virulence factors and is increasingly found in hospital and community settings, the organism is increasingly associated with biofilm infections in diabetic foot ulcers. With limited options, a novel treatment strategy is required, and the use of lytic phages presents a promising alternative. In this study, lytic phage vB_SmaS_BCU-1 was isolated from soil and propagated with a clinical S. maltophilia strain, isolated from a diabetic foot ulcer. Morphology characterisation and genomic analysis revealed it is a siphophage belonging to the family Casjenviridae, genus Sanovirus. Phage vB_SmaS_BCU-1 is a dsDNA virus consisting of 57,752 bp containing 75 open reading frames, with no virulence or antibiotic resistance genes found. vB_SmaS_BCU-1 was stable at a range of temperatures (4-55 °C) & pH values (4-12), has a short latent period (30 min), a large burst size (150 PFU/cell) and efficient adsorption. The phage demonstrated lysis of planktonic cells and can significantly reduce biofilm biomass. In a human fibroblast co-culture model, the phage exhibited no cytotoxicity, protected cells from bacterial-induced damage and significantly reduced the bacterial load.