Viridans streptococci in infective endocarditis: species distribution and susceptibility to antibiotics

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Abstract
A method for the speciation of viridans streptococci (non-groupable) is described. The major identification criteria are based on the reactions to a series of biochemical tests, including acid production in lactose, inulin, raffinose, mannitol and sorbitol, hydrolysis of arginine, esculin and Na hippurate, and production of polysaccharides in 5% sucrose media. A total of 450 strains was isolated from blood cultures, 183 of which were from confirmed cases of subacute endocarditis. The latter were identified as follows (%): Streptococcus sanguis I (25·7), S. mitis (19·7). S. sanguis II (19·7), S. mutans (17·5), S. milleri (12). S. morbillorium (3·2) and S. salivarius (2·2). Susceptibility to antibiotics was studied for 129 of these strains: 68% were susceptible to all drugs tested, 20% were resistant only to tetracycline, 4% only to penicillin (MIC = 0.5–4 μg ml–1) and 8% were multiply resistant (tetracycline, macrolides and related drugs, chloramphenicol, penicillin, high-level resistance to kanamycin and/or streptomycin [MIC = 1000–80.00 μg ml−1]).

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