Antimicrobial susceptibility of clinical isolates of aerobic Gram-positive cocci and anaerobic bacteria in 2004

The activity of antibacterial agents against aerobic Gram-positive cocci (28 species, 1,020 strains) and anaerobic bacteria (21 species, 170 strains) isolated from clinical specimens in 2004 at 16 clinical facilities in Japan were studied using either broth microdilution or agar dilution method. The ratio of methicillin-resistant strains among Staphylococcus aureus was 63.1% and Staphylococcus epidermidis 84.2%, suggesting that resistant strains were isolated at high frequency. Vancomycin(VCM), linezolid(LZD), and quinupristin/dalfopristin (QPR/DPR) had good antibacterial activity against methicillin-resistant S. aureus and methicillin-resistant S. epidermidis, with MIC₉₀s of ≤2 μg/mL. The ratio of penicillin(PC) intermediate and resistant strains classified by mutations of PC-binding proteins among Streptococcus pneumoniae was 86.5%. Cefpirome, ceftriaxone, carbapenem antibiotics, VCM, and teicoplanin had MIC₉₀s of ≤1 μg/mL against PC-intermediate and resistant S. pneumoniae strains. VCM and teicoplanin also showed good antibacterial activity against Enterococcus faecalis and Enterococcus faecium with MIC₉₀s of ≤2 μg/mL, and no resistant strains were detected. Of E. faecium strains, 7.8% showed intermediate and 23.4% resistant to LZD or QPR/DPR. Among anaerobes, carbapenems showed good activity against Peptococcaceae, Bacteroides spp., and Prevotella spp. The susceptibility of Bacteroides spp. other than Bacteroides fragilis to these antibiotics, however, appeared to be lowered, necessitating well-focused surveillance studies.