Mecanismos implicados en la colonización y la epidemicidad del clon de alto riesgo "Klebsiella pneumoniae ST15"

Abstract

Klebsiella pneumoniae ST15 is a high-risk clone with high genetic plasticity carrying a wide diversity of antimicrobial resistance genes. It is implicated in the production of hospital outbreaks worldwide and it has a high capacity to colonize the gastrointestinal tract, which is a major risk factor for the subsequent development of an infection. This Doctoral Thesis deals with the study of the mechanisms involved in the pathogenesis of K. pneumoniae ST15 with the aim of searching for new therapeutic targets and alternative strategies for the management of infections caused by this highrisk clone. For this purpose, we used as a model an epidemic clone of K. pneumoniae ST15 isolated during a large outbreak at the University Hospital of A Coruña. Comparative analysis of its genome against other clones belonging to different K. pneumoniae STs allowed us to identify specific genomic features of this clone that could be involved in its success as a pathogen. We found that clone ST15 possesses two virulence factors related to adherence that are not present in the rest of the STs analysed. A chaperone-usher pili system, the Kpi system, and a two-component secretion system, the FhaB/FhaC system, have been identified and characterized for the first time in K. pneumoniae. These systems are directly related to the highly adherent phenotype displayed by the epidemic clone ST15, as they are involved in the ability of this clone to adhere to different eukaryotic cells and form biofilm. In addition, the Kpi and FhaB/FhaC systems are closely related to this ST and confer greater fitness. On the other hand, it has been demonstrated that the Kpi system has a determining role both in the ability shown by this epidemic clone to colonize the 24 gastrointestinal tract in a murine model of colonization, and in its pathogenic potential in a model of infection in Galleria mellonella. Considering that the two systems characterized in this study are clearly associated with the high-risk clone ST15, they can be considered optimal biomarkers to identify this clone specifically. In this context, both systems could be used as targets to detect K. pneumoniae ST15 with high sensitivity and specificity. Finally, we have obtained and characterized a saline extract of Vaccinium corymbosum with a high polyphenol content. This extract inhibits intestinal eukaryotic cell adhesion and biofilm formation in the strain Kp3380. The antiadhesive effect produced by this extract significantly reduces intestinal colonization by K. pneumoniae in a murine model.