Multicenter assessment of the linezolid spectrum and activity using the disk diffusion and Etest methods: report of the Zyvox(R) antimicrobial potency study in Latin America (LA-ZAPS)

RESUMO

Linezolid was the first clinically applied member of the new antimicrobial class called the oxazolidinones. These agents have a powerful spectrum of activity focussed against Gram-positive organisms including strains with documented resistances to other antimicrobial classes. We conducted a multicenter surveillance (Zyvox Antimicrobial Potency Study; ZAPS) trial of qualifying Gram-positive isolates from 24 medical centers in eight countries in Latin America. The activity and spectrum of linezolid was compared to numerous agents including glycopeptides, quinupristin/dalfopristin, beta-lactams and fluoroquinolones when testing 2,640 strains by the standardized disk diffusion method or Etest (AB BIODISK, Solna, Sweden). The linezolid spectrum was complete against staphylococci (median zone diameter, 29 - 32 mm), as was the spectrum of vancomycin and quinupristin/dalfopristin. Among the enterococci, no linezolid resistance was detected, and the susceptibility rate was 93.1 - 96.4. Only the vancomycin-susceptible Enterococcus faecium strains remained susceptible (92.8) to quinupristin/dalfopristin. Marked differences in the glycopeptide resistance patterns (van A versus van B) were noted for the 22 isolates of VRE, thus requiring local susceptibility testing to direct therapy. Streptococcus pneumoniae and other species were very susceptible (100.0) to linezolid, MIC(90) at 0.75 microg/ml. Penicillin non-susceptible rate was 27.7 and erythromycin resistance was at 17.4. Other streptococci were also completely susceptible to linezolid (MIC(90), 1 microg/ml). These results provide the initial benchmark of potency and spectrum for linezolid in Latin American medical centers. Future comparisons should recognize that the oxazolidinones possess essentially a complete spectrum coverage of the monitored staphylococci, enterococci and streptococcal isolates in 2000-2001. This positions linezolid as the widest spectrum empiric choice against multi-resistant Gram-positive cocci, a spectrum of activity greater than available glycopeptides and the streptogramin combination.