Mechanisms of the Development and Maintenance of Salmonella Gallbladder Carriage

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Salmonellae are Enterobacteriaceae that cause a spectrum of diseases in humans and animals, including enteric (typhoid) fever and gastroenteritis. Typhoid fever caused primarily by Salmonella enterica serovar Typhi (S. Typhi), results in a life-threatening systemic disease that is responsible for significant morbidity and mortality annually worldwide. Approximately 5% of individuals infected with S. Typhi become chronic carriers with the gallbladder (GB) as the site of persistence. S. Typhi is a human- restricted pathogen, therefore asymptomatic carriers represent a critical reservoir for further spread of disease. We have demonstrated that gallstones (GSs) aid in the development and maintenance of GB carriage in a mouse model (utilizing S. Typhimurium, which causes a typhoid-fever like disease in mice) and in humans, serving as a substrate to which Salmonellae attach and form a protective biofilm. Thus, biofilm formation is a key step in the establishment of carriers. Traditional antibiotic therapies are usually incapable of clearing chronic S. Typhi infections, as the biofilm phenotype renders the bacteria tolerant to the mechanisms of these drugs. Thus, the identification of novel therapeutics capable of targeting S. Typhi biofilms is necessary in order to eliminate chronic carriage and eradicate the disease. Towards this end, our group has identified four small molecules and two antibodies capable of inhibiting and/or disrupting Salmonella biofilms in vitro. We advance two of the small molecules in this proposal, JG-1 and M4, that both inhibit and disrupt biofilms in vitro and reduce GB bacterial numbers in vivo. We hypothesize that the use of these anti-biofilm compounds in conjunction with an antibiotic will more effectively inhibit and disrupt Salmonella biofilms in vivo in our mouse model of chronic carriage when compared to the administration of antibiotic therapy alone. In Aim 1, we will assess the efficacy of these anti-biofilm compounds at preventing and treating chronic infection compared to traditional antibiotics alone by utilizing our established mouse model of typhoidal chronic carriage. We will also measure important pharmacokinetic and tolerability parameters of these compounds. In order to elucidate the mechanisms by which these compounds antagonize Salmonella biofilms, in Aim 2 we will identify the specific bacterial target(s) of each compound by enriching for mutants exhibiting compound resistance and by performing direct pull-downs of targets from bacterial lysates. Structure activity relationships and derivatives with enhanced physiochemical and biological properties will be generated in Aim 3. In summary, we propose an investigation into the safety, efficacy, and mechanisms of novel anti-biofilm compounds to prevent and treat chronic infections by typhoidal Salmonella. To our knowledge this study will be the first attempt (utilizing subject experts in anti-biofilm medicinal chemistry and Salmonella chronic infection) to specifically target Salmonella biofilm formation in vivo as a means of combating chronic carriage.