Antimicrobial susceptibility of Gemella haemolysans isolated from patients with subacute endocarditis.

Gemella haemolysans, a member of the family Streptococcacae, was isolated from patients with subacute endocarditis. The minimal inhibitory concentrations of 21 antimicrobial agents for five strains of the organism were determined. All strains were highly sensitive to penicillin G and ampicillin. Cefotaxime was the most active cephalosporin tested. All strains were sensitive to vancomycin, chloramphenicol and rifampin. Four strains were sensitive to tetracycline and erythromycin. All strains demonstrated a low level of resistance to aminoglycosides and were highly resistant to sulfonamides and trimethoprim. Killing curves and checker-board titration demonstrated synergism between penicillin G and streptomycin or gentamicin, and also between vancomycin and streptomycin or gentamicin. The results suggest that penicillin G combined with an aminoglycoside can be recommended for the treatment of subacute endocarditis caused by Gemella haemolysans.