Susceptibility of methicillin-resistant Staphylococcus aureus to vancomycin, teicoplanin, linezolid, pristinamycin and other antibiotics.
BACKGROUND
Methicillin-resistant Staphylococcus aureus is a major nosocomial pathogen worldwide. Vancomycin is the traditional drug of choice, but decreasing susceptibility to vancomycin and other glycopeptides has been reported since 1996.


OBJECTIVE
To test the in vitro activity of linezolid (oxazolidinone) and other antimicrobial agents against MRSA isolates recovered from hospitalized patients.


METHODS
We tested 150 MRSA isolates recovered from hospitalized patients. The minimal inhibitory concentration of vancomycin, teicoplanin, pristinamycin (quinupristin-dalforistin) and linezolid was determined by the Etest method. Susceptibility to other antibiotics was tested by the disk diffusion method.


RESULTS
All isolates were sensitive to vancomycin, teicoplanin, pristinamycin, and linezolid. The MIC90 was 2.0 microg/ml for vancomycin and teicoplanin (range 0.5-2.0 microg/ml and 0.125-2.0 microg/ml, respectively), and 0.5 microg/ml for pristinamycin and linezolid (range 0.125-0.75 microg/ml and 0.125-0.5 microg/ml, respectively). Of the other antibiotics, fusidic acid showed the best in vitro activity, with 96.7% susceptibility, associated with trimethoprim/sulfamethoxazole (85.8%) and minocycline (84%). Penicillin was associated with the lowest susceptibility (1.3%), associated with ofloxacin (3%) and erythromycin (14%). An increase in the minimal inhibitory concentration value of vancomycin was associated with a significant decrease in resistance to TMP-SMZ (P < 0.01) and an apparent increase in resistance to other antibiotics.


CONCLUSIONS
The excellent in vitro activity of linezolid and its reported in vivo effectiveness renders it an important therapeutic alternative to vancomycin in the treatment of MRSA infection.
Samra
Zmira
Z
National Staphylococcus Center, Department of Microbiology, (Beilinson Campus), Petah Tiqva, Israel. zsamra@clalit.org.il
Ofer
Orit
O
Shmuely
Haim
H
D000081:Acetamides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000890:Anti-Infective Agents / Q000494:pharmacology*; D006801:Humans; D000069349:Linezolid; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D023303:Oxazolidinones / Q000494:pharmacology*; D025762:Pristinamycin / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects*; D017334:Teicoplanin / Q000494:pharmacology*; D014640:Vancomycin / Q000494:pharmacology*
D000081:Acetamides; D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D023303:Oxazolidinones; D025762:Pristinamycin; D017334:Teicoplanin; D014640:Vancomycin; D000069349:Linezolid