Inducing effective phagocytic clearance of non-motile bacteria

Dartmouth College, Hanover NH

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Abstract

Abstract The Gram-negative bacteria, which include Pseudomonas aeruginosa, cause substantial morbidity and mortality: bacterial pneumonia, septicemia and chronic disease account for ~15% of the total deaths in the USA. Therefore, it is imperative that we develop a better cellular and molecular understanding of the host interactions with bacterial pathogens, how bacteria avoid or manipulate the host?s response, and to develop new strategies to prevent disease and improve patient care. For a variety of Gram-negative bacteria, flagellar swimming motility has been demonstrated to be required to initially infect the host. However, the bacteria must become non-motile to persist during clinical chronic infection. A well-described example is that the loss of P. aeruginosa motility directly correlates with bacterial persistence, increased bacterial burdens, and increased disease severity in Cystic Fibrosis patients. Our lab was the first to demonstrate that the observed loss of bacterial motility, regardless of loss of flagellar expression, enables P. aeruginosa to evade phagocytic clearance by macrophages and neutrophils both in vitro and in vivo. Additionally, sessile P. aeruginosa, especially upon formation of microcolonies or biofilms, become tolerant to standard-of-care antibiotics: this is reflected in ineffective eradication of bacteria from chronically infected patients following antibiotic treatments. These two traits ? phagocytic evasion and antibiotic tolerance ? enable non-motile P. aeruginosa to persist as chronic infections despite our best current treatments, and thus there is an obvious and pressing need for a novel intervention. Therefore the central goal of this proposal is to elucidate a novel and effective methodology that will induce the phagocytic clearance of non-motile P. aeruginosa. Our recently published studies that mechanistically demonstrate that non-motile bacteria avoid triggering the PI3K/Akt-dependent phagocytic response identify a potential therapeutic opportunity that guides the central hypothesis of this proposal: that activation of the Akt-dependent phagocytic pathway will promote the therapeutic clearance of the non- motile P. aeruginosa that persist in chronic infection. Based on our preliminary data, we propose a single, focused Specific Aim that tests the feasibility of our evidence-supported premise: that we can induce the phagocytic clearance of sessile bacteria. Achievement of this Aim will identify a molecular signaling pathway within host phagocytes, and a methodology by which to induce this pathway, which can potentially be harnessed to effect the therapeutic clearance of the non-motile, antibiotic-tolerant bacteria present in chronic infections.