ANTIMICROBIAL SUSCEPTIBILITY OF VIRIDANS GROUP STREPTOCOCCI IN TAIWANWITH AN EMPHASIS ON THE HIGH-RATES OF RESISTANCE TO PENICILLIN AND MACROLIDES IN STREPTOCOCCUS-ORALIS

The in-vitro susceptibilities of 13 antimicrobial agents were determin ed for 207 isolates of viridans group streptococci recovered from pati ents with significant infections in Taiwan during 1995 and 1997. Varia ble degrees of susceptibility existed among nine species. High-level p enicillin resistance (MIC greater than or equal to 4.0 mg/L) was found most frequently in Streptococcus oralis (35%), followed by Streptococ cus mitis (20%) and Streptococcus salivarius (8%). However, S. salivar ius showed the lowest rate of susceptibility to penicillin (50%). Macr olide resistance also occurred most frequently in S. oralis isolates ( 55%) but in none of Streptococcus mutans. Penicillin and macrolides te nded to be less active against isolates recovered from noninvasive sit es than against those isolated from invasive sites. Imipenem was the m ost active beta-lactam against penicillin-resistant isolates. Ofloxaci n, vancomycin and teicoplanin showed good in-vitro activity against al l isolates, with MIC(90)s of 2, 1 and 0.25 mg/L, respectively. None of these isolates displayed high-level resistance to gentamicin and most isolates were susceptible to chloramphenicol. These results indicate the species-related variability of susceptibility, especially to penic illin, macrolides and tetracycline. In addition to S, mitis, S. oralis also displayed high rates of resistance to penicillin and macrolides. The difference in susceptibilities between species of viridans strept ococci indicates the importance of accurate identification and the nee d for continuing surveillance of antimicrobial resistance.