ABSTRACTThe effort to discover novel phages infectingStaphylococcus epidermidiscontributes to both the development of phage therapy and the expansion of genome-based phage phylogeny. Here, we report the genome of anS. epidermidis-infecting phage, Lacachita, and compare its genome with those of five other phages with high sequence identity. These phages represent a novel siphovirus genus, which was recently reported in the literature. The published member of this group was favorably evaluated as a phage therapeutic agent, but Lacachita is capable of transducing antibiotic resistance and conferring phage resistance to transduced cells. Members of this genus may be maintained within their host as extrachromosomal plasmid prophages, through stable lysogeny or pseudolysogeny. Therefore, we conclude that Lacachita may be temperate and members of this novel genus are not suitable for phage therapy.IMPORTANCEThis project describes the discovery of a culturable bacteriophage infectingStaphylococcus epidermidisthat is a member of a rapidly growing novel siphovirus genus. A member of this genus was recently characterized and proposed for phage therapy, as there are few phages currently available to treatS. epidermidisinfections. Our data contradict this, as we show Lacachita is capable of moving DNA from one bacterium to another, and it may be capable of maintaining itself in a plasmid-like state in infected cells. These phages’ putative plasmid-like extrachromosomal state appears to be due to a simplified maintenance mechanism found in true plasmids ofStaphylococcusand related hosts. We suggest Lacachita and other identified members of this novel genus are not suitable for phage therapy.