vB_KpM_GP-7: a novel myovirus targeting capsule-deficient, phage-resistant Klebsiella pneumoniae

The nosocomial spread of multidrug-resistant (MDR) Klebsiella pneumoniae strains represents a significant public health threat, highlighting the urgent need to identify alternative therapeutic strategies. One possible approach is the use of bacteriophages, especially as cocktails made-up by viruses targeting different bacterial receptors. Components of these cocktails can be obtained by using, in phage-screening procedures, strains that have acquired resistance to previously identified phages. Here, we report the identification of vB_KpM_GP-7, a novel lytic phage isolated from urban wastewater using a capsule-deficient, phage-resistant mutant of a clinical MDR K. pneumoniae strain belonging to the Sequence Type (ST) 258 clade II. vB_KpM_GP-7 is able to infect a broad spectrum of in vitro selected capsule-deficient K. pneumoniae strains, including some belonging to STs different from its parental strain. The phage revealed a strictly lytic replication cycle, with a latent period of 25 minutes and an average burst size of 45 particles/ infected cell and was stable in a wide pH range (4 – 11) and after incubation at 60° C for an hour. Genomic analysis identified that vB_KpM_GP-7 is a myovirus belonging to the Marfavirus genus, with a 169,127 bp linear dsDNA genome in which genes associated with lysogeny or known virulence factors are absent. Frequency of resistance emergence by using high multiplicity of infection was overall low, suggesting a limited risk of rapid resistance development. Altogether, these data highlight that vB_KpM_GP-7 could be a promising candidate for further investigation for its integration into phage cocktails to fight infections caused by MDR K. pneumoniae strains.