[In vitro activity of tigecycline against methicillin-resistant staphylococci].

Glycylcyclines are novel semisynthetic group of antibiotics that have been produced by substitution of glycylamido group at position 9 of tetracyclines. Tigecycline derived from minocycline is the first member of glycylcyclines. This new antibiotic has a broad spectrum of activity against variety of gram-positive and gram-negative bacteria and is not affected by known tetracycline resistance mechanisms. The aim of this study was to investigate the in-vitro activity of tigecycline as well as vancomycin, linezolid, quinupristin-dalfopristin and trimethoprim-sulphamethoxazole (TMP-SMX) against methicillin-resistant staphylococci isolated from clinical specimens of adult patients in Hacettepe University Hospital. For this purpose 127 Staphylococcus aureus (MRSA) and 42 coagulase negative staphylococci (MRCNS) which had been shown to be resistant to methicillin by disc diffusion method performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines, were evaluated. In these isolates minimum inhibitory concentration (MIC) values of tigecycline were detected by E-test; susceptibilities to linezolid, quinupristin-dalfopristin, TMP-SMX were detected by disc diffusion test. All of the isolates were searched for decreased susceptibility to vancomycin by agar screening method and MIC values of vancomycin were detected by E-test for the strains that grew on vancomycin agar plates. The range of MIC values of tigecycline were 0.032-1 microg/ml for the 127 MRSA isolates (MIC50 0.25 microg/ml, MIC90 0.75 microg/ml) and were 0.047-1 microg/ml (MIC50 0.25 microg/ml, MIC90 0.5 microg/ml) for the MRCNS isolates. All staphylococcal isolates were found to be susceptible to vancomycin, linezolid and quinupristin-dalfopristin. TMP-SMX resistance was detected in 7 (5.5%) MRSA and 26 (60.5%) MRCNS isolates. The results of this study demonstrated very good in-vitro activity of tigecycline against both MRSA and MRCNS isolates in our hospital. A remarkable finding of the present study was demonstration of the quite low rate of TMP-SMX resistance among MRSA isolates whereas MRCNS isolates showed high rate of resistance.