Ruoff, Kathryn L. Francis Blake Bacteriology Laboratories, Department of Microbiology and Molecular Genetics, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.
Last reviewed:January 2019
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A genus of spherical or ovoid bacteria (some being notably pathogenic) that are characteristically arranged in pairs or in chains resembling strings of beads. Numerous bacteria are assigned to the genus Streptococcus. They are commonly referred to as streptococci and can be isolated from humans and other animals. Many members of the streptococci constitute part of the normal microbial flora of the mouth, throat, intestine, and skin and are harmless commensal forms; in contrast, other streptococci are highly pathogenic (Fig. 1). The cells are gram-positive (that is, they retain a violet color when Gram's stain is applied) and can grow either anaerobically or aerobically, although they cannot utilize oxygen for metabolic reactions. Glucose and other carbohydrates serve as the sources of carbon and energy for growth. All members of the genus lack the enzyme catalase (which catalyzes the decomposition of hydrogen peroxide into molecular oxygen and water). See also: Bacteria; Bacteriology; Carbohydrate; Enzyme; Glucose; Human microbiota; Medical bacteriology; Microbiome; Oxygen; Pathogen
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