In-vitro activity of 29 antimicrobial agents against penicillin-resistant and -intermediate isolates of Streptococcus pneumoniae

Antibiotic resistance among isolates of Streptococcus pneumoniae is increas ing worldwide. Optimal therapy, though unknown, should be guided by in-vitr o susceptibility testing. Currently, vancomycin is the only approved antibi otic that is universally active against multi-resistant S. pneumoniae. In-v itro activities were determined far 29 antimicrobial agents against 22 peni cillin-intermediate S. pneumoniae (PISP) and 16 penicillin-resistant S. pne umoniae (PRSP) isolates. MICs were determined in cation-adjusted Mueller-Hi nton broth with 3% lysed horse blood in microtitre trays. Antimicrobial cla sses tested included cephalosporins, penicillin, aminopenicillins, macrolid es, quinolones, carbapenems and other antimicrobial agents. Among the class es of antimicrobial agents tested, wide differences in susceptibility were demonstrated for both PISP and PRSP. Of the cephalosporins, ceftriaxone and cefotaxime demonstrated the best in-vitro activity for both PISP and PRSP. Of the quinolones, clinafloxacin and trovafloxacin showed the greatest in- vitro activity. Rifampicin and teicoplanin demonstrated excellent in-vitro activity, Promising in-vitro results of newer agents, such as quinupristin/ dalfopristin, ramoplanin, teicoplanin and linezolid may justify further eva luation of these agents in clinical trials.