Antimicrobial susceptibility of clinical isolates of aerobic Gram-negative bacteria in 2004

We determined MICs of antibacterial agents against 1,248 clinical strains of aerobic Gram-negative bacteria (19 genus or species) isolated at 16 Japanese facilities in 2004. MICs were determined using mostly broth microdilution method and antibacterial activity was assessed. Antibacterial susceptibility of Enterobacteriaceae to most β-lactams was comparable to that described in our previous report on isolates in 2002. Strains producing extended-spectrum β-lactamases(ESBL) accounted for 2.5% of Escherichia coli, 0% of Klebsiella spp., and 9.2% of Proteus spp. Notably, 16.7% of Proteus mirabilis was found to produce ESBL. Most antibacterial agents showed good activity against Moraxella catarrhalis. Among Haemophilus influenzae, 9.3% produced β-lactamase and 57.7% were β-lactamase-negative ampicillin-resistant strains when classified by penicillin-binding protein 3 mutation. Although few antibacterial agents against Pseudomonas aeruginosa have potent activity, only three agents-tobramycin, doripenem, and amikacin-showed an MIC₉₀ of ≤8 μg/mL. Of all P. aeruginosa strains, 8.9% were resistant to seven or more agents of ten antipseudomonal agents, a decrease compared to results reported in 2002. Against other glucose-non-fermentative Gram-negative bacteria, the activity of most antibacterial agents was similar to that in 2002.