[Characteristics of "Streptococcus mutans" from endocarditis and susceptibility to antimicrobial agents (author's...

Strains of Streptococcus mutans were isolated from blood cultures of ten patients with endocarditis. Nine of these patients had a typical clinical picture of subacute bacterial endocarditis, with fever, weakness, heart murmur and multiple positive blood cultures. All the patients had previous valvular heart diseases; only in three cases the initiating event involved some type of dental manipulations which where supposed as the source of infection. The major criteria for recognizing S. mutans were colony morphology on blood agar, characteristic extracellular polysaccharide production in 5% sucrose broth, acid formation in mannitol and sorbitol broth, and the failure of antigenic extracts of S. mutans to react with streptococcal group antisera. The susceptibility to antimicrobial agents was tested by the diffusimetric method with susceptibility disks. All the strains were susceptible to penicillin G, erythromycin, pristinamycin, lincomycin and tetracycline, and resistant to streptomycin and gentamicine.