Regulation of Shigella Infection via the Gut Microbiome - ABSTRACT Shigella infection causes shigellosis, a gastroenteric illness characterized by bloody diarrhea. Shigella infection affects over 80-165 million individuals per year worldwide, resulting in approximately 600,000 deaths. Countries with developing sanitation systems are heavily affected, with young children being primary victims of the disease. Currently, there are no vaccines or prophylactic options for Shigellosis. Although drugs like ciprofloxacin are often used to treat Shigella infection, antibiotic-resistant strains are on the rise, resulting in increased prevalence and mortality. Susceptibility to Shigella infection is influenced by both the immune system and the gut microbiome, the complex community of resident microbes in the intestine. However, the mechanism of protection is not well understood. Recently, data from our lab and others show the important role of the gut microbiome in protection against Shigella infection. For example, Bacteroides thetaiotaomicron (also known as B. theta) of phylum Bacteroidetes, a prominent member of the human gut microbiome, produces outer membrane vesicles that reduce Shigella virulence in culture. We have also identified that excreted products from B. thetaiotaomicron and the gut bacterium Enterococcus faecalis can decrease growth of Shigella. These data reveal the gut microbiome’s propensity to act as therapeutic agents. To continue investigating the role of the gut microbiome on Shigellosis based on these promising findings, I propose that by using bacterial culturing and innovative mouse models, we will determine how “healthy” gut bacteria can mitigate Shigella infection. In this proposed study, I will: 1) examine the effects of various gut bacteria on growth and virulence of Shigella through growth curve assays and a fluorescent reporter plasmid for virulence; 2) utilize the gnotobiotic mouse model to determine effects of defined gut bacterial communities on Shigella colonization, cell invasion, and disease outcomes. Narrowing which bacteria help mitigate infection can contribute to the discovery of protective microbes and inspire the development of probiotic candidates for disease prophylaxis for high-risk individuals. Training: I am well suited to conduct these studies due to my expertise in studying prophylactic options for bacteria-caused gastrointestinal diseases such as C. difficile infection. Recently, I have translated my previous skills into studying probiotic solutions for Shigellosis. In my preliminary research, I have determined a handful of Bacteroidetes-related bacteria that can reduce Shigella growth. I have also recently been able to establish Shigella infection in the germ-free mouse. This proposal will build on my prior knowledge of infectious gastrointestinal diseases and my preliminary research findings on the gut microbiome effects on Shigella. Moreover, this research will lay the groundwork for my overarching long-term goal of establishing my own interdisciplinary research group at a top research university focusing on defining the role of the gut microbiome in various debilitating human disorders and diseases. This research training plan will prepare me to develop into an independent investigator to lead impactful research that integrates microbiology, molecular biology, and biochemistry. With the guidance of my sponsor and mentorship committee, I will be well-equipped to meet these goals. Dr. Ashley Wolf’s lab has expertise in infectious diseases, gut microbiome, gnotobiotic animal models that, in conjunction with resources and collaborations at UC Berkeley, will provide an environment for success for me to conduct this research.
