Distribution of resistant gram-positive organisms across the census regions of the United States and in vitro activity of tigecycline, a new glycylcycline antimicrobial

Background Gram-positive isolates were collected from 76 medical centers within the 9 census regions across the United States. Methods Antimicrobial susceptibilities were determined according to Clinical and Laboratory Standards Institute guidelines. Results Vancomycin resistance among Enterococcus faecium isolates varied from 45.5% (New England) to 85.3% (East South Central). The lowest concentrations at which 90% of the isolates were inhibited (MIC90) were for tigecycline (0.06-0.12 μg/mL) and for linezolid (2-4 μg/mL). Methicillin-resistant Staphylococcus aureus (MRSA) varied from 27.4% (New England) to 62.4% (East South Central). All MRSA were susceptible to tigecycline, linezolid, and vancomycin. Penicillin-nonsusceptible Streptococcus pneumoniae ranged from 23.3% in the Pacific region to 54.5% in the East South Central region. Tigecycline, imipenem, levofloxacin, linezolid, and vancomycin all maintained MIC90 of ≤1 μg/mL against penicillin-nonsusceptible S pneumoniae in vitro, irrespective of region. Conclusion This study demonstrates the variable rate of antimicrobial-resistant gram-positive organisms in the United States. Tigecycline may make a useful addition to the antimicrobial armamentarium.