Streptococcus

Excerpt

The genus Streptococcus , a heterogeneous group of Gram-positive bacteria, has broad significance in medicine and industry. Various streptococci are important ecologically as part of the normal microbial flora of animals and humans; some can also cause diseases that range from subacute to acute or even chronic. Among the significant human diseases attributable to streptococci are scarlet fever, rheumatic heart disease, glomerulonephritis, and pneumococcal pneumonia. Streptococci are essential in industrial and dairy processes and as indicators of pollution.

The nomenclature for streptococci, especially the nomenclature in medical use, has been based largely on serogroup identification of cell wall components rather than on species names. For several decades, interest has focused on two major species that cause severe infections: S pyogenes (group A streptococci) and S pneumoniae (pneumococci). In 1984, two members were assigned a new genus - the group D enterococcal species (which account for 98% of human enterococcal infections) became Enterococcus faecalis (the majority of human clinical isolates) and E faecium (associated with a remarkable capacity for antibiotic resistance).

In recent years, increasing attention has been given to other streptococcal species, partly because innovations in serogrouping methods have led to advances in understanding the pathogenetic and epidemiologic significance of these species. A variety of cell-associated and extracellular products are produced by streptococci, but their cause-effect relationship with pathogenesis has not been defined. Some of the other medically important streptococci are S agalactiae (group B), an etiologic agent of neonatal disease; E faecalis (group D), a major cause of endocarditis, and the viridans streptococci. Particularly for the viridans streptococci, taxonomy and nomenclature are not yet fully reliable or consistent. Important members of the viridans streptococci, normal commensals, include S mutans and S sanguis (involved in dental caries), S mitis (associated with bacteremia, meningitis, periodontal disease and pneumonia), and “S milleri” (associated with suppurative infections in children and adults). There remains persistent taxonomic confusion regarding “S milleri.” These and other streptococci of medical importance are listed inTable 13-1by serogroup designation, normal ecologic niche, and associated disease.