Targeting Pathogen Altruism to Prevent Bacterial Infections in Animals

Antibiotics fail because the selective pressure to produce resistance in pathogenic bacteria is immense: there can be no more stringent selection than death. A solution to the problem of antimicrobial resistance is thus to target the altruistic behaviors of bacterial pathogens rather than their survival. In nature, an individual bacterium may engage in an altruistic act that leads to its own demise because that act promotes the survival of its clonal siblings, thus propagating its own genetic information by proxy. Importantly, only a small fraction of a population can exhibit such behavior without fitness loss to the population overall. An intervention that blocks altruistic acts has two significant consequences: it eliminates an important advantage to the population, and it presents an insurmountable barrier to the proliferation of resistant mutants (i.e. mutation toward fatality). It is thus a superior antimicrobial approach; targeting a pathogen function for which mutation to resistance is highly detrimental and, in fact, often fatal.The long-term goal of our work is to identify practical interventions to prevent infections in livestock without the use of conventional antimicrobials. Our recent work has provided an opportunity to develop dietary supplements for production animals to reduce the carriage of the important pathogen Salmonella. There is compelling evidence that Salmonella carriage requires the penetration of the intestinal epithelium (termed invasion). Invasion is an altruistic act, leading to the death of that small fraction of total population that invades, but creating a chemical environment in the intestine that supports the growth of surviving Salmonella. We have shown that specific compounds, related to the weak acids commonly produced in the intestine, reduce invasion through their post-translational control of invasion regulators of the AraC family. Our central hypothesis is thus that blocking invasion through the inactivation of these regulators will prevent long-term colonization of animals by Salmonella by a means that is not subject to the selective pressure for resistance that readily occurs with antimicrobial use.We will test this hypothesis by accomplishing these objectives:Objective 1. Determine the mechanism by which chemical inhibitors affect Salmonella invasion. We hypothesize that repressive signaling molecules bind directly to invasion regulators and propose here to use biochemical and genetic means to investigate this direct method of protein control.Objective 2. Identify drug-like inhibitors of Salmonella invasion using a high-throughput chemical library screen. We will test and characterize a library of some 1250 bio-active lipid compounds for their inhibition of invasion and suitability as dietary supplements for production animals.Objective 3. Determine the oral efficacy of selected compounds in reducing Salmonella carriage and shedding in chickens. Chickens are an important reservoir of Salmonella, as they carry the pathogen without clinical signs. Here we will identify compounds that demonstrate promise as preventative drugs using the chicken carriage model.Objective 4. Assess the frequency and consequences of resistance to invasion inhibitors. To determine whether our approach is free of the essential pitfall of traditional antimicrobials, we will screen drug-like inhibitor compounds for the frequency at which resistant mutants are produced, and the in vivo fitness of those mutants.