In Vitro Activity of BL-S640 Against Gram-Negative Bacilli and Staphylococcus aureus Compared with Activity of Four Other Semisynthetic Cephalosporins

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Abstract
The in vitro activity of BL-S640 (cefatrizine) was determined against 674 recent clinical isolates of Staphylococcus aureus and Enterobacteriaceae . Activity against S. aureus was less than that of cephapirin, cephalothin, and cefazolin, but greater than that of cephalexin. Activity against gram-negative isolates was variable: BL-S640 was slightly less potent than cefazolin against Escherichia coli and Klebsiella , but more active than the other compounds. As for the more resistant gram-negative genera, BL-S640 was significantly superior to the control cephalosporins. The effect of inoculum size on the antibacterial activity was moderate for most organisms except Enterobacter, Providencia stuartii , and indole-positive Proteus , the median minimal inhibitory concentrations of which were 6 to 27 times lower when determined with a 10 −4 -diluted culture compared with the undiluted one. The stability in aqueous solution at 37 C was remarkably high at the lower pH values, but low at the neutral point.