A Kayvirus Distant Homolog of Staphylococcal Virulence Determinants and VISA Biomarker Is a Phage Lytic Enzyme.

Staphylococcal bacteriophages of the Kayvirus genus are candidates for therapeutic applications. One of their proteins, Tgl, is slightly similar to two staphylococcal virulence factors, secreted autolysins of lytic transglycosylase motifs IsaA and SceD. We show that Tgl is a lytic enzyme secreted by the bacterial transport system and localizes to cell peripheries like IsaA and SceD. It causes lysis of E. coli cells expressing the cloned tgl gene, but could be overproduced when depleted of signal peptide. S. aureus cells producing Tgl lysed in the presence of nisin, which mimics the action of phage holin. In vitro, Tgl protein was able to destroy S. aureus cell walls. The production of Tgl decreased S. aureus tolerance to vancomycin, unlike the production of SceD, which is associated with decreased sensitivity to vancomycin. In the genomes of kayviruses, the tgl gene is located a few genes away from the lysK gene, encoding the major endolysin. While lysK is a late phage gene, tgl can be transcribed by a host RNA polymerase, like phage early genes. Taken together, our data indicate that tgl belongs to the kayvirus lytic module and encodes an additional endolysin that can act in concert with LysK in cell lysis.

The Ability of Lytic Staphylococcal Podovirus vB_SauP_phiAGO1.3 to Coexist in Equilibrium With Its Host Facilitates the Selection of Host Mutants of Attenuated Virulence but Does Not Preclude the Phage Antistaphylococcal Activity in a Nematode Infection Model.

Phage vB_SauP_phiAGO1.3 (phiAGO1.3) is a polyvalent Staphylococcus lytic podovirus with a 17.6-kb genome (Gozdek et al., 2018). It can infect most of the Staphylococcus aureus human isolates of dominant clonal complexes. We show that a major factor contributing to the wide host range of phiAGO1.3 is a lack or sparcity of target sites for certain restriction-modification systems of types I and II in its genome. Phage phiAGO1.3 requires for adsorption ß-O-GlcNAcylated cell wall teichoic acid, which is also essential for the expression of methicillin resistance. Under certain conditions an exposure of S. aureus to phiAGO1.3 can lead to the establishment of a mixed population in which the bacteria and phages remain in equilibrium over multiple generations. This is reminiscent of the so called phage carrier state enabling the co-existence of phage-resistant and phage-sensitive cells supporting a continuous growth of the bacterial and phage populations. The stable co-existence of bacteria and phage favors the emergence of phage-resistant variants of the bacterium. All phiAGO1.3-resistant cells isolated from the phage-carrier-state cultures contained a mutation inactivating the two-component regulatory system ArlRS, essential for efficient expression of numerous S. aureus virulence-associated traits. Moreover, the mutants were unaffected in their susceptibility to infection with an unrelated, polyvalent S. aureus phage of the genus Kayvirus. The ability of phiAGO1.3 to establish phage-carrier-state cultures did not preclude its antistaphylococcal activity in vivo in an S. aureus nematode infection model. Taken together our results suggest that phiAGO1.3 could be suitable for the therapeutic application in humans and animals, alone or in cocktails with Kayvirus phages. It might be especially useful in the treatment of infections with the majority of methicillin-resistant S. aureus strains.

Complete Genome Sequences of Two Novel Staphylococcus aureus Podoviruses of Potential Therapeutic Use, vB_SauP_phiAGO1.3 and vB_SauP_phiAGO1.9.

Here, we report the genome sequences of two Staphylococcus aureus phages belonging to the family Podoviridae and subfamily Picovirinae, vB_SauP_phiAGO1.3 and vB_SauP_phiAGO1.9, which were isolated from Warsaw sewage. Analysis of their genomes provides valuable information about the diversity of phages belonging to the genus Rosenblumvirus and their genes that undergo evolutionary adaptation to cells of different host strains.

Phage Therapy: What Have We Learned?

In this article we explain how current events in the field of phage therapy may positively influence its future development. We discuss the shift in position of the authorities, academia, media, non-governmental organizations, regulatory agencies, patients, and doctors which could enable further advances in the research and application of the therapy. In addition, we discuss methods to obtain optimal phage preparations and suggest the potential of novel applications of phage therapy extending beyond its anti-bacterial action.