Yi Xu
Yi Xu, PhD
Associate Professor
Center for Infectious and Inflammatory Diseases
Contact
Translational Medical Sciences
2121 W. Holcombe Blvd
Houston,
TX
77030
yi-xu1@tamu.edu
Phone: 713.677.7570
Fax: 713.677.7576
Biography
Our current research activities focus on understanding the pathogenic mechanism of Streptococcus gallolyticus subsp. gallolyticus (Sgg). Sgg is a gram-positive opportunistic pathogen that causes life-threatening bacteremia and infective endocarditis (IE). It is also strongly associated with colorectal cancer (CRC). My lab was the first to demonstrate that Sgg actively promotes the development of colon tumors, elevating a long-stranding clinical association to a functional causal role of Sgg in tumor development. Despite its medical importance, the pathogenic mechanism of Sgg remains poorly understood. Our recent studies have demonstrated that a type VII secretion system of Sgg plays a key role in pathogenesis. Currently we are interested in understanding the mechanism underlying following key steps in Sgg pathogenesis: 1) colonization of the intestinal epithelium, 2) modulation of intestinal homeostasis in normal and tumor-bearing colons, and 3) dissemination from the gastrointestinal tract to the circulatory system.Keywords: bacterial pathogenesis, infectious diseases, virulence, colorectal cancer, microbiome, microbiota, type VII secretion system, gastrointestinal tract
Education and Training
- University of Texas Health Science Center at Houston, PhD, 1998
Research Interests
- Bacteria and cancer; host-pathogen interactions; immune evasion. Our lab is interested in the broad area of bacterial-host interactions. The manifestation and progression of infectious diseases are determined by the combined effects of bacterial factors and host reactions. Understanding these interactions is critical for combating infectious diseases. Furthermore, some of the bacterial – host interactions may cause alterations in host physiological or cellular processes that contribute to other types of diseases including cancer. Currently there are two lines of research in the lab. The role of bacteria in the development of cancer It has been recognized that the gut microbiome has a profound influence in the health and disease status of the human body. Specific bacterial species or dysbiosis of the microbiome have been found to contribute to the development of colorectal cancer (CRC). This bacteria-CRC connection suggests a potential paradigm shift in the way CRC is detected, treated and managed. To realize this potential, a clear understanding of specific microbial components involved in the development of CRC and their mechanism of action is important. In our lab, we focus on Streptococcus gallolyticus subsp. gallolyticus (Sgg), previously known as S. bovis biotype I. This organism is known to strongly correlate with CRC. Patients with Sgg infections have elevated risks of developing colorectal adenoma/adenocarcinoma. Using a combination of cell cultures and mouse models, we recently demonstrated that Sgg actively promotes colon tumor growth. Analysis of tumor tissues and matched normal colon tissues from CRC patients further showed that the majority of tumor tissues are positive for Sgg and that Sgg preferentially associates with tumor tissues compared to normal tissues. These exciting discoveries highlight the importance of Sgg, as it not only has a strong clinical correlation with CRC but is also functionally important for the development of CRC. Our current focus is to understand the role of Sgg in the development of CRC in more specific details, and to elucidate the mechanisms underlying the tumor-promoting effect of Sgg. Bacterial manipulation of the complement system. The complement system is not only the first line of defense against microorganisms, but also links the innate immune system to the adaptive immune system. It is not surprising that manipulation of the complement system is a strategy adopted by several bacterial pathogens. We found that certain proteins on the surface of spores of Bacillus anthracis and other related organisms interact with components in the complement system. We are interested in understanding the molecular details of these interactions and how they affect the outcome of infections.