Susceptibility of viridans streptococci of 27 antimicrobial agents.

One hundred and eighty strains of viridans Streptococci (Str. mitis, Str. salivarius, Str. MG, Str. SBE, Str. bovis, Str. equinus and Str. uberis) were isolated from mouth and upper respiratory tract secretions of humans at random in different parts of Poland. These strains were tested for susceptibility to 27 antimicrobial agents. Analysis of results was performed with special reference to bacterial endocarditis, which is caused mostly by these microorganisms. At low minimal inhibitory concentrations, most effective antibiotics appeared amoxycillin, clindamycin, azidocillin, cephaloridine, ampicillin, erythromycin and penicillin G. Susceptibility to other penicillins and cephalosporins was much less pronounced. Small part of strains was highly susceptible to tetracyclines, whereas all other antimicrobial agents were practically ineffective.