Molecular and Cellular Microbiology (Department of Microbiology)
We have been studying oral bacteria related to dental caries and periodontal diseases. Recently, we widened the scope of our research to general microbiology, since a number of microbes use the oral cavity as the portal of entry to cause general diseases and we consider it important to elucidate the general microbiology of dental diseases. In particular, we are investigating the virulence factors of oral and general streptococci, as analyses of the molecules involved could lead to development of novel preservation and treatment procedures.
■ Research Outline
I. Streptococcus pyogenes
S. pyogenes is known as a human pathogen that causes streptococcal pharyngitis as well as more severe invasive infections, including necrotizing fasciitis, sepsis, and streptococcal toxic shock syndrome. We have identified several adhesins/invasins of S. pyogenes and are investigating how S. pyogenes organisms invade epithelial cells. In addition, we reported that infiltrating neutrophils were not observed at sites of S. pyogenes infection and investigated how S. pyogenes inhibits the complement immune system.
A number of antibiotics including penicillin are effective for S. pyogenes infection, however, antibiotic treatment failure in cases of streptococcal pharyngitis have been reported. Thus, we are also attempting to elucidate the mechanisms associated with recurrent streptococcal pharyngitis.
II. Streptococcus pneumoniae
S. pneumoniae is a major pathogen of community-acquired pneumonia, while it also causes meningitis, otitis, and septicemia, with high rates of incidence of morbidity and mortality throughout the world. S. pneumoniae localizes in the human upper respiratory tract. In recent years, resistance by S. pneumoniae to penicillin and other antibiotics has been increasing worldwide, and thus the present “antibiotic era” might be coming to a terminal phase. To resolve this problem and help usher in a new “post-antibiotic era,” we have been analyzing the virulence factors of S. pneumoniae and are investigating S. pneumoniae vaccine candidates.
S. sanguinis is a member of the oral streptococci group. It is the first bacterium to colonize tooth surfaces, where it functions as an initiator by forming dental plaque, which leads to the development of dental caries and periodontal diseases. S. sanguinis has been reported to be closely related to infective endocarditis, which is frequently caused by oral bacteria entering the bloodstream following trauma. In a recent study, we identified a virulence factor that plays important roles in bacterial colonization, and speculated that this molecule may be a reasonable target to prevent bacterial infection and disease progression.