Isolation and Characterization of Six Novel Phages.

Introduction: , a human and animal pathogen, is the primary etiologic agent of bovine liver abscesses and a driving factor for prophylactic antibiotic use in the fed cattle industry. Considering calls to reduce agricultural antibiotic use, we isolated phages capable of killing as an alternative or complementary biocontrol strategy.

Methods: Six novel phages (φFN37, φRTG5, φKSUM, φHugo, φPaco, and φBB) were isolated from rumen fluid or ruminal isolates and subjected to host range testing on both subspecies. Four subspecies, phages, were tested for cross-resistance and host growth inhibition individually and in pairs. Additionally, genomic sequencing, annotation, and analysis were performed.s.

Results: Four of six isolated phages were able to form lysogens, although all six contained lysogeny-related genes. φKSUM and φBB, did not form lysogens and were able to infect both subspecies. Four phages could infect 8L1 (a liver abscess model challenge strain) . Genomic analysis showed that these phages belong to class with genome sizes ranging from 35 kbp to 111 kbp and GC values ranging from 26% to 36% and have extremely limited similarity to other deposited phage genomes infecting or other genera.

Conclusions: Although all phages isolated contained sequences bearing similarities to genes implicated in lysogeny, the four selected for use in cocktails showed potential in inhibiting host growth, with several demonstrating promising attributes for biocontrol and therapeutic applications. Phage cocktails that may offer enhanced antibacterial activity were also identified, indicating the potential of some lysogenic phages to be adapted for biocontrol or therapeutic purposes when lytic phages are difficult to obtain.