ZAAPS International Surveillance Program (2007) for linezolid resistance: results from 5591 Gram-positive clinical isolates in 23 countries

The 2007 ZAAPS Program reports the results from the 6th year of oxazolidinone (linezolid) resistance surveillance among Gram-positive pathogens from 23 nations. For 2007, a total of 5591 organisms were systematically sampled from Asia, Australia, Canada, Europe, and Latin America including Staphylococcus aureus (3000 isolates, 38.2% methicillin resistant), coagulase-negative staphylococci (CoNS, 716 isolates), enterococci (906 isolates), Streptococcus pneumoniae (452 isolates), viridans group streptococci (155 isolates), and β-hemolytic streptococci (362 isolates). The overall linezolid MIC distribution (MIC50 and MIC90 at 1 and 2 μg/mL, respectively) was unchanged since 2002. At published linezolid breakpoints (≤2 μg/mL), all streptococci were susceptible; however, resistance was observed very rarely among S. aureus (0.03%), CoNS (0.28%), and the enterococci (0.11%, 0.55% intermediate). These oxazolidinone-nonsusceptible isolates occurred in Ireland, Italy, China, and Brazil (9 strains), and the rate was not increased since 2006. The detected mechanism of resistance was G2576 target mutations; no cfr-mediated patterns were observed. Clonal outbreaks with patient-to-patient dissemination were documented in 1 Italian site. Linezolid appears to retain excellent activity against monitored Gram-positive pathogens at a level of >99.8%.