Acquisition of novel antibiotic resistance genes by the bacterial predator Bacteriovorax sp. As-1

This study reports the isolation and characterization of Bacteriovorax sp. As-1, a predatory bacterium recovered from the gut of oxytetracycline-treated juvenile rainbow trout (Oncorhynchus mykiss). Phylogenetic and genomic analysis indicate it is closely related to Bacteriovorax stolpii DSM 12778T, although genomic metrics suggest it represents a new species. Like other Bdellovibrio-and-like organisms, Bacteriovorax sp. As-1 exhibits predatory activity against Aeromonas salmonicida, significantly reducing its prey viability by nearly six orders of magnitude. However, whole genome sequencing revealed the presence of multiple antibiotic resistance genes, including those previously associated with decreased susceptibility to tetracyclines, aminoglycosides, sulfonamides, and fluoroquinolones, located within genomic islands, and flanked by insertion sequences, suggesting acquisition via horizontal gene transfer (HGT). In addition to these, mutations were also detected in gyrA gene that confer resistance to ciprofloxacin. Phenotypic assays confirmed Bacteriovorax sp. As-1 has increased antibiotic resistance as compared to Bx. stolpii DSM 12778T. This study presents a natural predatory strain carrying IS-linked ARG clusters consistent with HGT, highlighting their potential role as reservoirs of resistance determinants in antibiotic-enriched environments.