Role of Bacterial Surface Structures on the Interaction of Klebsiella pneumoniae with Phagocytes

Abstract

Phagocytosis is a key process of the immune system. The human pathogen Klebsiella pneumoniae is a well known example of a pathogen highly resistant to phagocytosis. A wealth of evidence demonstrates that the capsule polysaccharide (CPS) plays a crucial role in resistance to phagocytosis. The amoeba Dictyostelium discoideum shares with mammalian macrophages the ability to phagocytose and kill bacteria. The fact that K. pneumoniae is ubiquitous in nature and, therefore, should avoid predation by amoebae, poses the question whether K. pneumoniae employs similar means to counteract amoebae and mammalian phagocytes. Here we developed an assay to evaluate K. pneumoniae-D. discoideum interaction. The richness of the growth medium affected the threshold at which the cps mutant was permissive for Dictyostelium and only at lower nutrient concentrations the cps mutant was susceptible to predation by amoebae. Given the critical role of bacterial surface elements on host-pathogen interactions, we explored the possible contribution of the lipopolysaccharide (LPS) and outer membrane proteins (OMPs) to combat phagoyctosis by D. discoideum. We uncover that, in addition to the CPS, the LPS O-polysaccharide and the first core sugar participate in Klebsiella resistance to predation by D. discoideum. K. pneumoniae LPS lipid A decorations are also necessary to avoid predation by amoebae although PagP-dependent palmitoylation plays a more important role than the lipid A modification with aminoarabinose. Mutants lacking OMPs OmpA or OmpK36 were also permissive for D. discoideium growth. Except the LPS O-polysaccharide mutants, all mutants were more susceptible to phagocytosis by mouse alveolar macrophages. Finally, we found a correlation between virulence, using the pneumonia mouse model, and resistance to phagocytosis. Altogether, this work reveals novel K. pneumoniae determinants involved in resistance to phagocytosis and supports the notion that Dictyostelium amoebae might be useful as host model to measure K. pneumoniae virulence and not only phagocytosis.

Modeling Klebsiella pneumoniae Pathogenesis by Infection of the Wax Moth Galleria mellonella

“…Moreover, differential immunostaining experiments revealed that G. mellonella hemocytes did not engulf K. pneumoniae 52145. Similar observations were made by infecting human cell cultures and mouse macrophages with this pathogen (35,36,51,58). Strikingly, the G. mellonella model also recapitulates additional aspects of the interplay between K. pneumoniae and the lung innate immune system.…”

“…Previously, we showed that ompA and ompK36 mutants express levels of CPS similar to that in K. pneumoniae 52145 and that they are attenuated in the mouse pneumonia model (33,36,56). Like those of the lipid A mutants, the LD 50 s of the OMP mutants were higher than that of the wild type (Table 3).…”

“…Conversely, this suggests that K. pneumoniae tries to counteract the induction of these host defense responses. Indeed, we and others have shown that, in sharp contrast to wild-type strains, attenuated mutant strains activate an inflammatory program, ultimately favoring their clearance (33)(34)(35)(36)(37).…”

Klebsiella pneumoniae: Going on the Offense with a Strong Defense

“…Further studies showed that an ompK36 deletion mutant can colonize the liver, but cannot persist, following intraperitoneal injection (345). Likewise, an ompK36 deletion mutant could not infect the lungs to WT levels in a pneumonic infection model (354). Further studies evaluating a classical K. pneumoniae strain with and without ompK36 showed that mice infected intraperitoneally or intranasally with this deletion mutant experienced significantly less mortality (345,354).…”

“…Likewise, an ompK36 deletion mutant could not infect the lungs to WT levels in a pneumonic infection model (354). Further studies evaluating a classical K. pneumoniae strain with and without ompK36 showed that mice infected intraperitoneally or intranasally with this deletion mutant experienced significantly less mortality (345,354). One mechanism by which OmpK36 may contribute to virulence in vivo is by preventing phagocytosis, as demonstrated by the increased uptake of an ompK36 deletion mutant by human neutrophils (345).…”