In vitro activity of linezolid as assessed through the 2013 LEADER surveillance program

The 2013 LEADER surveillance program monitored the in vitro activity of linezolid and comparator agents against Gram-positive bacteria at 60 medical centers in the United States. A total of 7183 pathogens were contributed from 6 predetermined pathogen groups. The groups were Staphylococcus aureus, coagulase-negative staphylococci, enterococci, Streptococcus pneumoniae, β-hemolytic streptococci, and viridans group streptococci. The MIC90 value for each of the 6 pathogen groups was 1 μg/mL. Susceptibility of "all organisms" to linezolid was 99.83%. Only 12 isolates (2 S. aureus, 3 Staphylococcus epidermidis, 1 Streptococcus sanguinis, 5 Enterococcus faecium, and 1 Enterococcus faecalis) were nonsusceptible to linezolid (0.17%). Three of these (2 S. aureus and 1 E. faecium) harbored the cfr resistance mechanism. The findings indicate that linezolid activity remains stable, although there are examples of clonal dissemination within several monitored institutions.