Microbiology - Streptococcus and Enterococcus

Summary The streptococci and enterococci are a large and diverse group of gram positive catalase negative coccoid bacteria. Identification of members within this group is complicated, with beta haemolytic species being separated primarily by their lancefield serotype. Alpha and gamma haemolytic species are separated by methods including resistance to antibiotics. Enterococci form lancefield serotype D, even though they are alpha and gamma haemolytic. S. pyogenes (group A streptococcus) is the most important pathogen of the streptococci with many virulence factors. The similarity of it’s antigens to human tissue can result in auto-immune like diseases, and complicates the search for an effective vaccine against it. S. agalactiae is associated with lethal neonatal disease. Preventative measures have resulted in much reduction in it’s incidence. Viridans streptococci are important opportunistic pathogens. They form biofilms and are a leading cause of endocarditis as well dental caries. S. pneumoniae is the second most significant of the streptococcal pathogens, with many mechanisms for avoiding the immune response. It’s immunogenic polysaccharide capsule has allowed the development of effective vaccines. Enterococci are responsible for many difficult to treat hospital acquired infections. Though they have only a few virulence factors, they are of great concern since they have much resistance to antibiotics which may also be transferred to other bacteria.