It is gram-positive cocci arranged in tetrads or in clusters. On blood agar, colonies are surrounded by a greenish hemolysis. A. viridans stands Streptococcus and staphylococcus by microaerophilic respiratory type. Catalase is variable.
Long considered a single air pollutant, A. viridans sometimes behaves as an opportunistic responsible for hospital infections in fragile patients. The predisposing causes are diabetes, immunosuppressants, alcoholism and bladder stasis.
Insensitive to penicillin G, A. viridans is very sensitive to ampicillin, cephalosporins, and trimethoprim. Sensitivity to gentamicin is low.
Two species are described: G. haemolysans and G. morbillorum.
The type species Cemella haemolysans was isolated in cases of infective endocarditis. It is also found in the upper respiratory tract, eyes and intestine. These anaerobic motionless bacteria that may appear Gram (-), isolated or grouped in pairs or short chains. They are catalase (-) and oxidase (-) G. haemolysans creates hemolysis of erythrocytes of rabbit or horse. This bacterium is susceptible to common antibiotics except to aminoglycosides and sulfonamides.
Leuconostoc – Pediococcus:
Leuconostoc and Pediococcus are characterized by a high-level resistance to vancomycin (> 512 mcg / ml).Leuconostoc can act as an opportunistic pathogen and Pediococcus can be selected and isolated especially in stool in patients undergoing heavy antibiotic . Some guidance characters distinguish these genera (Table I).
Stomatococcus mucilaginosus is isolated in almost 1C 0% of oral pharyngeal samples plated on blood agar. This germ, often unrecognized, saprophytic host of the throat and mouth, is sometimes responsible for opportunistic infections or bacterial transient. That is why the main characters identifying this germ should not be ignored: they are Gram-positive cocci in clusters, producing abundant capsular material having little or no catalase activity, reducing nitrate to nitrite , hydrolyzing esculin and gelatin and producing acetoin. These bacteria grow on blood agar or Columbia medium, but not in the presence of 5% NaCl. They form white colonies, non-hemolytic and adhering to the agar.