Isolation of Bacteriophages Lytic to Fusobacterium necrophorum Subspecies necrophorum from Bovine Ruminal Fluid and City Sewage

Fusobacterium necrophorum subspecies necrophorum, a resident of the rumen, is the causative agent of bovine liver abscesses. Currently, tylosin, a macrolide, is used in the feed to reduce liver abscesses. Because macrolides are medically important antibiotics, their use in food animal production is of public health concern. There is significant interest in finding antimicrobial alternatives. Bacteriophages that lyse subsp. necrophorum have the potential to replace tylosin. Our objective was to isolate bacteriophages lytic to subsp. necrophorum. Pooled ruminal fluid from slaughtered cattle and pooled sewage samples were collected and incubated overnight with lysine, and subsp. necrophorum strains and filtrates were spotted on F. necrophorum lawns. Phage plaques were harvested and purified. Bacteriophage isolation frequencies were compared between sample types, sampling dates, and necrophorum strains. Overall relative frequency of isolated bacteriophages lytic to subsp. necrophorum was 17.1%. The frequency of bacteriophage isolation ranged from 0 to 25.4% for ruminal fluid, and from 13.7 to 32.0% for sewage. Isolation frequency was significantly higher in sewage than in ruminal fluid samples (p < 0.01). Isolation rates varied significantly between necrophorum strains. Sewage was a rich source of bacteriophages lytic to necrophorum, which have the potential to be used to prevent liver abscesses.