Antimicrobial susceptibility of viridans group streptococci

A total of 68 viridans group streptococci, including 31 Streptococcus sanguis, 12 S. mitis, 3 S. salivarius, and 8 S. milleri from blood, and an additional 14 S. milleri from abscesses and normally sterile sites, were tested against penicillin, amoxicillin, cefazolin, ceftriaxone, meropenem, clindamycin, quinupristin/dalfopristin, rifampin, levofloxacin, ofloxacin, vancomycin, and gentamicin with the microdilution method. The susceptibility rates for S. sanguis were: penicillin, 74%; amoxicillin, 84%; ceftriaxone, 94%; clindamycin, 87%, and vancomycin, 100%. The susceptibility rates for S. mitis were: penicillin, 42%; amoxicillin, 67%; ceftriaxone, 58%; clindamycin, 100%; and vancomycin, 100%. The susceptibility rates for S. milleri were: penicillin, 100%, amoxicillin, 100%; ceftriaxone, 100%, clindamycin, 100%; and vancomycin, 100%. Two of the three isolates of S. salivarius were susceptible to penicillin, amoxicillin, and ceftriaxone; all were susceptible to clindamycin and vancomycin. Levofloxacin, quinupristin/dalfopristin, and rifampin were highly active against all isolates.