"Viridans group streptococci, including Streptococcus sanguis and Streptococcus mutans, are gram-positive cocci in chains. They produce alpha-hemolytic colonies and are catalase negative. Growth is resistant to optochin, in contrast to pneumococci, which are inhibited. Colonies are not dissolved by bile. Endocarditis is the most important disease, and brain abscess can occur, especially in mixed infections with mouth anaerobes. S. mutans is implicated in dental caries. The habitat is the human oropharynx, and the organism enters the bloodstream during dental procedures. It is a low-virulence organism. Bacteremia from dental procedures spreads the organism to damaged heart valves, and the organism is protected from host defenses within vegetations. No known toxins have been identified. A glycocalyx composed of polysaccharide enhances adhesion to heart valves. Diagnosis is made by Gram-stained smear and culture. On blood agar, colonies are alpha-hemolytic. Growth is not inhibited by bile or optochin, in contrast to pneumococci. Serologic tests are not useful. Treatment is penicillin G with or without an aminoglycoside. Penicillin is used to prevent endocarditis in patients with damaged or prosthetic heart valves who undergo dental procedures."