EMERGENCE OF HIGH-RATES OF ANTIMICROBIAL RESISTANCE AMONG VIRIDANS GROUP STREPTOCOCCI IN THE UNITED-STATES

Three hundred fifty-two blood culture isolates of viridans group strep tococci obtained from 43 U,S, medical centers during 1993 and 1994 wer e characterized, Included were 48 isolates of ''Streptococcus milleri, '' 219 S. mitis isolates, 29 S, salivarius isolates, and 56 S. sanguis isolates, High-level penicillin resistance (MIG, greater than or equa l to 4.0 mu g/ml) was noted among 13.4% of the strains; for 42.9% of t he strains, penicillin MICs were 0.25 to 2.0 mu g/ml (i,e,, intermedia te resistance), In general, amoxicillin was slightly more active than penicillin, The rank order of activity for five cephalosporins versus viridans group streptococci was cefpodoxime = ceftriaxone > cefprozil = cefuroxime much greater than cephalexin, The percentages of isolates resistant (MIC, greater than or equal to 2 mu g/ml) to these agents w ere 15, 17, 18, 20, and 96, respectively, The rates of resistance to e rythromycin, tetracycline, and trimethoprimsulfamethoxazole were 12 to 38%, Resistance to either chloramphenicol or ofloxacin was uncommon ( i,e., <1%). In general, among the four species, S, mitis was the most resistant and ''S, milleri'' was the most susceptible.