A Unique Isolation of a Lytic Bacteriophage Infected Bacillus anthracis Isolate from Pafuri, South Africa

Bacillus anthracis is a soil-borne, Gram-positive endospore-forming bacterium and the causative agent of anthrax. It is enzootic in Pafuri, Kruger National Park in South Africa. The bacterium is amplified in a wild ungulate host, which then becomes a source of infection to the next host upon its death. The exact mechanisms involving the onset (index case) and termination of an outbreak are poorly understood, in part due to a paucity of information about the soil-based component of the bacterium's lifecycle. In this study, we present the unique isolation of a dsDNA bacteriophage from a wildebeest carcass site suspected of having succumbed to anthrax. The aggressively lytic bacteriophage hampered the initial isolation of B. anthracis from samples collected at the carcass site. Classic bacteriologic methods were used to test the isolated phage on B. anthracis under different conditions to simulate deteriorating carcass conditions. Whole genome sequencing was employed to determine the relationship between the bacterium isolated on site and the bacteriophage-dubbed Bacillus phage Crookii. The 154,012 bp phage belongs to Myoviridae and groups closely with another African anthrax carcass-associated Bacillus phage WPh. Bacillus phage Crookii was lytic against B. cereus sensu lato group members but demonstrated a greater affinity for encapsulated B. anthracis at lower concentrations (<1 × 10⁸ pfu) of bacteriophage. The unusual isolation of this bacteriophage demonstrates the phage's role in decreasing the inoculum in the environment and impact on the life cycle of B. anthracis at a carcass site.