The rise of antibiotic resistance in bacteria represents a large threat to human health. Consequently, new therapies are urgently needed. Bacteriophages (phages) are viruses that infect and kill bacteria. The use of phage therapy, either as a complement or alternative to antibiotics, may provide an attractive means to treat infection and curb the rise of antibiotic resistance. In this study, we have focused our efforts on the isolation and investigation of phages targeting clinically relevant pathogens, Bacillus cereus and Serratia marcescens. Genomic and ultrastructural investigation of JWP1, a novel siphoviridae phage targeting B. cereus, a gram positive spore-forming bacterium, revealed a distinctive genome organisation and highly elaborate and unique tail structure. We designed and implemented a CRISPR-Cas9 system in B. cereus to demonstrate that JWP1 is in fact a flagellotropic phage, that is, it utilises the host flagellum as the site of attachment. Specific deletion of the host flagellin genes was shown to be protective against phage infection. Serratia marcescens is an opportunistic, gram negative, nosocomial pathogen. We have isolated four novel siphoviridae phages that infect clinical isolates of S. marcescens and described their genomes. In an effort to understand how phage-host interactions and spontaneous resistance of these S. marcescens hosts to phages may occur in a clinical setting, we are currently employing mutagenesis studies followed by whole-genome sequencing. This will allow us to determine host to factors essential for phage infectivity and efficacy. Ultimately, the isolation of phages to clinically relevant pathogens and understanding their infectivity will lead to effective treatment options in an era of rising antimicrobial resistance.