Synergistic removal of Staphylococcus aureus biofilms by using a combination of phage Kayvirus rodi with the exopolysaccharide depolymerase Dpo7.

Abstract

Bacteriophages have been shown to penetrate biofilms and replicate if they find suitable host cells. Therefore, these viruses appear to be a good option to tackle the biofilm problem and complement or even substitute more conventional antimicrobials. However, in order to successfully remove biofilms, in particular mature biofilms, phages may need to be administered along with other compounds. Phage-derived proteins, such as endolysins or depolymerases, offer a safer alternative to other compounds in the era of antibiotic resistance. This study examined the interactions between phage Kayvirus rodi with a polysaccharide depolymerase (Dpo7) from another phage (Rockefellervirus IPLA7) against biofilms formed by different Staphylococcus aureus strains, as determined by crystal violet staining, viable cell counts and microscopy analysis. Our results demonstrated that there was synergy between the two antimicrobials, with a more significant decreased in biomass and viable cell number with the combination treatment compared to the phage and enzyme alone. This observation was confirmed by microscopy analysis, which also showed that polysaccharide depolymerase treatment reduced, but did not eliminate extracellular matrix polysaccharides. Activity assays on mutant strains did not identify teichoic acids or PNAG/PIA as the exclusive target of Dpo7, suggesting that may be both are degraded by this enzyme. Phage adsorption to S. aureus cells was not significantly altered by incubation with Dpo7, indicating that the mechanism of the observed synergistic interaction is likely through loosening of the biofilm structure. This would allow easier access of the phage particles to their host cells and facilitate infection progression within the bacterial population.