In Vitro Activity and Beta-Lactamase Stability of BL-S786 Compared with Those of Other Cephalosporins

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Abstract
In vitro activity of BL-S786, a new parenterally semisynthetic cephalosporin, was investigated against 570 bacterial isolates. BL-S786 inhibited most Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis , and Salmonella . It inhibited some Enterobacter and indole-positive Proteus , but it was less active against these later species than was cefamandole, cefuroxime, or cefoxitin. It was not active against Serratia marcescens, Pseudomonas aeruginosa , or Bacteroides fragilis . BL-S786 was the least active new cephalosporin tested against staphylococci and was less active than cephalothin against streptococcal species. The activity of BL-S786 was not altered by the type of assay medium nor by 50% serum. The size of the test inoculum altered the minimal inhibitory and bactericidal concentrations for inhibition of some organisms, particularly those with Richmond type I β-lactamases. BL-S786 was not hydrolyzed by the R-factor-mediated, Richmond type III β-lactamase, but it was hydrolyzed by type I β-lactamases.