Pseudomonas aeruginosa Carriage in the Gastrointestinal Tract

About This Grant

PROJECT SUMMARY Pseudomonas aeruginosa (PA) causes over 75,000 nosocomial infections each year in the U.S, and many of these lead to death. Our understanding of how patients acquire PA is rapidly evolving, and it is now apparent that the human gastrointestinal (GI) tract is a major reservoir. Although PA colonization of the GI tract is rare in healthy individuals, it is quite common in hospitalized patients receiving antibiotics. Once colonized, the GI tract contains large numbers of PA and is the source for subsequent spread to other body sites, which in turn leads to infections. This new understanding of PA ecology suggests that strategies to avoid or eradicate GI colonization by PA may prove efficacious in preventing a substantial portion of PA infections in hospitalized patients. In preliminary studies, we have established and characterized a mouse model of PA GI carriage. In this model, PA carriage is absent in untreated mice but occurs in high numbers (~108 CFU/gram feces) following a 7-day course of the antibiotic vancomycin. Interestingly, once established PA maintained carriage for up to 60 days despite cessation of vancomycin administration. We applied a bar-coded PA library to this mouse model and found that PA bacteria encountered a tight bottleneck in the stomach following orogastric inoculation. This bottleneck is largely due to gastric acid and can be overcome by co-inoculation with sodium bicarbonate. Interestingly, the surviving PA bacteria expanded rapidly in the small intestine and caecum over the next several days to numbers that far exceed the initial inoculum. These bacteria moved to the colon and were expelled in the feces. In this proposal, we propose to use this mouse model and corresponding data to better understand how PA establishes carriage. Our hypothesis is that PA produces carriage-facilitating factors that act in the stomach as well as those that act in the intestines and caecum. We propose to use several genetic approaches to identify these factors. These findings will lay the foundation for future studies designed to develop therapeutic inhibitors of these PA factors. Such inhibitors could potentially prevent or eradicate PA carriage and dramatically reduce the burden of multidrug PA infections.