Streptococcus pyogenes: disease and molecular pathogenesis 1

Welcome to another lecture in this series on bacterial pathogenesis. I'm Pat Cleary. I'm an Emeritus Professor of microbiology and immunology at the University of Minnesota Medical School. The focus of my lecture is Streptococcus pyogenes, a review of the diseases and the molecular pathogenesis of this organism.

I'd like to start out by giving you a brief overview of the genus Streptococcus. In the 1940s and 50s, Rebecca Lancefield subclassified streptococci using polysaccharide antigens produced by different strains of streptococcus as the antigenic markers for the identification of different species. She grouped streptococci into groups A through M. Since her work, however, microbiologists have given the streptococcus genus and species names. For example, Streptococcus pyogenes is also called group A Streptococcus. Many species have two names. They have a genus and a species name. But they are also referred to by their group names by some scientists and clinicians. I will try to use the genus and species names when possible. Important streptococcal species. Streptococcus pyogenes, or group A streptococcus, will be presented in detail later in the lecture. Streptococcus agalactiae, or group B streptococcus, is the cause of neonatal infections, newborn infections. I'll talk about them in a little more detail in the next slide. Streptococci dysgalactiae are a complicated collection of different strains of Streptococcus. Human isolates have been termed group C and G streptococcus, and they resemble Streptococcus pyogenes, both as far as the kinds of infections they cause and the virulence factors that they produce. Their classification is a little bit murky, so I prefer to continue to use the Lancefield designation of group C and G streptococcus. The dysgalactiae species are also animal pathogens. Streptococcus equi is an example. It causes sore throat and strangles in horses. The oral streptococci are also a complicated collection of species and subspecies. One that has been studied in some detail is Streptococcus mutans. It's the cause of dental caries. There are many other species in the oral cavity, and most seldom cause an infection. But if they happen to get into the bloodstream, they can, of course, cause sepsis and bacteremia and do a lot of damage. The streptococcus most often associated with invasive and serious infections is Streptococcus pneumoniae. Once again, this is a member of the normal flora, and many of us carry it in our nose and mouth without any problem. I'll say a little more about it in an upcoming slide.