In vitro activity of telithromycin, quinupristin/dalfopristin, linezolid and comparator antimicrobial agents against staphylococcus aureus clinical isolates

We have studied the prevalence of the different macrolide, lincosamide, streptogramin(B) (MLSB) phenotypes among clinical Staphylococcus aureus isolates erythromycin- and/or oxacillin-resistant; and also the activity of other antimicrobial agents including telithromycin, quinupristin/dalfopristin, linezolid, aminoglycosides, chloramphenicol and vancomycin. We found that 64.86% of S. aureus were oxacillin-resistant. While the most prevalent MLSB phenotype among methicillin-resistant S. aureus (MRSA) was constitutive MLSB (cMLS(B)) (83%), among methicillin-susceptible S. aureus (MSSA) it was inducible MLSB (iMLS(B)) (90%). Kanamycin resistance was more frequent than resistance to other aminoglycosides, being 100% for MRSA. Telithromycin was only active against iMLS(B), MS and erythromycin-susceptible isolates, although resistance rates were found among iMLS(B) MSSA (2.78%). Quinupristin/dalfopristin showed greater activity, with resistance rates of 2.5% for MRSA and 1.53% for MSSA. Both vancomycin and linezolid were fully active against all the isolates tested, with the highest MIC value being 2 mug/ml and 4 mug/ml, respectively. Among MRSA strains, 81.67% displayed resistance to five or more antimicrobials. This multiresistance was more frequently found among cMLS(B) strains (96.38% MRSA resistant to 6-9 agents).