In vitro activity of different ratios from matching cefotaxime/culbactam

Objective To study the in vitro activity of cefotaxime alone and combined at various ratios with sulbactam. Methods Minimal inhibitory concentration ( MIC ) were determined by the twofold agar dilution method against 636 clinical isolates from January 2000 to September 2002 in Beijing. Minimal bactericidal concentration ( MBC) were determined by the twofold broth dilution method against 34 strains. Four killing curves were drawn by determination colony forming unit counts at each time point. Results Sulbactam could decrease the gram negative bacilli resistance rates of cefotaxime. The MIC90 values of cefotaxime/sulbactam ( 1:1 and 2 : 1 ) against E. coli, Klebsiella pneumonia, Morganella morganii , Enterbacter cloacae, Enterobacter aerogenes, Serratia marcescens and Citrobacter freundii were 2-32 mg · L-1, lower than those of cefotaxime alone 4 ~ 32 times. Against gram positive cocci, the MIC90 values of cefotaxime/sulbactam against Staphylococcus epidermidis, Streptococcus pneumoniae and Streptococcus pyogenes were 0.13 -4 mg · L-1. Cefotaxime /sulbactam is a excellent bactericidal agent at various ratios. The MIC value of cefotaxime /sulbactam were effected at pH 5. 0 and pH 6. 0 against Staphylococcus aureus but it was unaffected by inoculum size and human serum. Conclusion Cefotaxime/sulbactam demonstrated great in vitro activity against clinical isolates and decreased resistance rates of β - lactamases producing strains. The antibacterial activity of cefotaxime /sulbactam (2:1) was comparable with that of 1:1.