Phage-resistance in Klebsiella pneumoniae clinical isolates may correlate to augmented clearance by phagocytes

Hospital-acquired infections sustained by Klebsiella pneumoniae (KP) strains are often very difficult to treat, mainly due to their frequent association with complex antibiotic resistance traits. Recently, the therapeutic use of bacteriophages against multidrug resistant bacterial infections is gaining a renewed interest, although its efficacy can be limited by the insurgence of phage-resistant strains, possibly making this approach inefficient and requiring constant efforts for new phage isolations. Since we have previously reported that a φBO1E resistant K. pneumoniae strain (BO-FR-1) shows a significant reduction of virulence in a Galleria mellonella model, in the present study we further evaluate the effect of phage resistance on host-pathogen interaction. Two KP phage-resistant mutants, BO-FR-1 and KP263-FR, have been generated in vitro using the KKBO-1 (Sequence Type 258) or KP263 (Sequence Type 147) clinical isolates. Bacterial clones were then used to infect monocyte-derived type-1 and type-2 macrophages obtained from healthy donors. Macrophage response was finally evaluated in terms of internalization index, intracellular killing capability, and inflammatory response. Our results show that both phage-resistant clones were significantly more prone to phagocytosis and to intracellular killing when compared to their parental strains, without showing significant differences in NF-kB activation. Although the insurgence of phage-resistance may represent a limitation for phage therapy, in the context of the interplay among phage, bacterial pathogen and host, it may be beneficial for the host by making bacterial strains more susceptible to innate immune response.