Study on antibacterial activities in vitro of different formulas cefotaxime/tazobactam

Objective To study the antibacterial activities in vitro of cefotaxime and different formulas of cefotaxime/tazobactam (1: 1, 3: 1, 5: 1 and 7:1). To evaluate the antibacterial activities of cefotaxime combining with tazobactam, and compare the effects of them. Methods Bacterial susceptibility testing was performed on 665 clinical iso-lates(β-lactmases-producing strains). Minimal inhibitory concentrations (MIC) were determined by use of agar dilution method, and the minimal bactericidal concentrations(MBC) were measured by broth dilution method. Results The antibacterial activities of cefotaxime/tazobactam were better than those of cefotaxime alone. MIC90 of cefotaxime/tazobactam with different formulas against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Shigella sonnei, Shigella flexneri and Salmonella strains was 0.25-16 mg/L, it was 1-32 times higher than that of cefotaxime alone. There were no significant differences among the effects of four different formulas of cefotaxime/tazobactam against gram-positive bacteria. MIC50 of cefotaxime/tazobactam with different formulas against Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus strains was 0.125-16 mg/L, it was as 1-32 times as that of cefotaxime alone. MIC90 was 1-32 mg/L, it was as 2-8 times as that of cefotaxime alone. Conclusion Cefotaxime/tazobactam with 5:1 ratio has higher antibacterial activity against most clinical isolates. It can reduce the drug resistance of β-lact-mases-producing bacteria. The antibacterial activity of cefotaxime/sulbactam (5:1) is equal to that of 1:1 and 3:1 ratio.