Dissecting the impact of gut evolution on Klebsiella pneumoniae pathogenesis.

Project Summary/Abstract Evolution is one of the most powerful forces influencing the success and failure of life. Successful adaptation to one's environment dictates the survivability of one's genetic lineage. This is especially true for pathogenic bacteria, which must adapt to many stresses to successfully colonize and infect their host, replicate, and spread to a new host. Despite its importance, there is a fundamental gap in our understanding of how evolution influences bacterial pathogenesis. This proposal's objective is to use an experimental evolution approach to determine the effects of evolution on the pathogenesis of the bacteria Klebsiella pneumoniae. K. pneumoniae frequently colonizes the gut, where it predominantly behaves as a commensal; however, gut colonization is the primary risk factor for K. pneumoniae disease and colonizing strains cause at least 80% of infections in colonized individuals. Thus, the gut is an important reservoir for infectious K. pneumoniae, which begs the question: how does evolution impact K. pneumoniae gut colonization and infection? This question is of high public health importance, as the prevalence of multi-drug-resistant K. pneumoniae and hypervirulent K. pneumoniae strains increases. Moreover, these strains are converging into dangerous multi-drug resistant, hypervirulent variants of K. pneumoniae. This necessitates a deeper understanding of K. pneumoniae gut colonization and infection. The central hypothesis of this proposal is that measurable, repeatable evolutionary events will enhance Kp gut fitness and modulate fitness during infection in a microbiome-dependent manner. We will test this hypothesis using two approaches: 1) we will assay K. pneumoniae evolution in the gut using a replay experiment; 2) Measure the impact of gut-derived mutations on K. pneumoniae pathogenesis. Using this approach, we will address the following questions: 1) does gut microbial community structure drive evolutionary outcomes?, 2) are K. pneumoniae strains experimentally evolved in the gut are fitter than their ancestors?, 3) does evolution in the gut enhance or restrict the ability of K. pneumoniae to colonize a novel host?, 4) does serial passage in the gut lead to reduced fitness during infection? The work in this proposal is innovative, as it requires a multidisciplinary approach to integrate experimental evolution with model systems that are directly relevant to human health. Completing this work will have a sustained positive impact through the identification and characterization of the mechanisms that underpin K. pneumoniae success in the gut and their impact on infection. This will help guide the development of decolonization interventions to reduce the risk of infection in individuals colonized by K. pneumoniae and potentially other opportunistic gut colonizers.