Biology of the group E streptococci: a review.

Group E streptococci are identified by a group antigen consisting of a cell wall rhamnose-glucose polymer. Other specific cell wall polysaccharides separate the group into at least six serotypes (II, IV, V, VI, VII and VIII). No species name has been accepted for the group E Streptococcus, although the organism is often designated as Streptococcus infrequens or S. lentus. Recently, the name S. porcinus has been proposed for a species that would include streptococci of groups E, P, U and V. Group E streptococci are fairly widely distributed in animals, especially swine, and are occasionally isolated from bovine milk. They cause streptococcal lymphadenitis of swine, an economically important disease, particularly in the United States. They do not appear to be the primary cause of any other disease or condition. The organisms enter the swine host through the mucosa of the pharyngeal or tonsillar surfaces, and are carried to the lymph nodes, primarily of the head and neck region, where abscesses are formed. Cell wall antigens induce the formation of serum agglutinins; a microtitration agglutination test, based upon reactions involving the type IV antigen, is considered a reliable test for detection of infection in animals. Antigenic components include group and type antigens, extra-cellular enzymes, and an antiphagocytic factor which may be associated with virulence of the organism and with protective immunity to streptococcal lymphadenitis of swine. This factor, a surface protein, develops on cells cultured in media fortified with serum, rendering the cells resistant to phagocytosis by porcine leukocytes. The classification, morphology, physiology, biochemistry and nutrition of the group E streptococci, and methods for their isolation, cultivation, and identification are reviewed.