In vitro activity of telithromycin and quinupristin/dalfopristin against methicillin-resistant coagulase-negative staphylococci with defined resistance genotypes.
We determined the activities of new antibiotics telithromycin (ketolide) and quinupristin/dalfopristin (streptogramins) against 88 macrolide and/or lincosamide resistant coagulase-negative staphylococci (CoNS) isolates with defined resistance gene status. Telithromycin susceptibility was determined only in erythromycin-sensitive isolates (15) indicating the same mechanisms of resistance. In contrast, all erythromycin-resistant isolates (73) were either constitutively resistant to telithromycin (13 isolates with constitutive erm genes) or demonstrated telithromycin D-shaped zone (60 isolates with inducible msr(A) and/or erm). However, the level of inducible resistance conferred by msr(A) (35 isolates) was borderline even after induction by erythromycin. No quinupristin/dalfopristin resistant isolate was observed if tested by disk-diffusion method (DDM) but 18 isolates were intermediate (MIC = 1-3 mg/L) and two isolates resistant (MIC = 8 mg/L) if tested by E-test. All these isolates were resistant to streptogramin A and harbored vga(A) gene (1 isolate) or vga(A)LC gene (19 isolates). MICs for quinupristin/dalfopristin were higher for isolates with combination of streptogramin A resistance and constitutive MLSB resistance (MIC = 3-8 mg/L in 4 isolates) than for streptogramin A-resistant isolates susceptible to streptogramin B (MIC = 0.5-2 mg/L in 16 isolates). In addition to S. haemolyticus, vga(A)LC was newly identified in S. epidermidis and S. warnerii indicating its widespread occurrence in CoNS. Misidentification of low-level resistant isolates by DDM may contribute to dissemination of streptogramin A resistance.
Novotná
G
G
Institute of Microbiology, Academy of Sciences of the Czech Republic, 142 20 Prague, Czechia. gnovotna@biomed.cas.cz
Spízek
J
J
Janata
J
J
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002981:Clindamycin / Q000494:pharmacology; D003030:Coagulase / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology; D048628:Ketolides / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology; D016106:Methicillin Resistance / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D013210:Staphylococcus / Q000187:drug effects*; D025364:Streptogramin A / Q000494:pharmacology; D025381:Streptogramin B / Q000494:pharmacology; D014769:Virginiamycin / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D003030:Coagulase; D048628:Ketolides; D018942:Macrolides; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D025381:Streptogramin B; D002981:Clindamycin; D004917:Erythromycin; D025364:Streptogramin A; C106791:telithromycin