BL-S786, a new parenteral cephalosporin. II. in vitro Antimicrobial activity comparison with six related cephalosporins.

Abstract

BL-S786 was compared by in vitro studies with 6 other parenteral cephalosporins (cefamandole, cefazolin, cefoxitin, cephaloridine, cephalothin and cephradine). The following parameters were assessed: Comparative MIC [minimum inhibitory concentrations] against a wide variety of bacterial isolates, MIC/MBC [minimum bactericidal concentration] comparisons and the effect of inoculum size on the MIC. BL-S786 showed the greatest antimicrobial activity against Klebsiella pneumoniae, Citrobacter diversus and Salmonella spp.; was equal to cefamandole against Escherichia coli, Enterobacter [E.] agglomerans and Proteus mirabilis and was 2nd to cefamandole against Shigella, Edwardsiella tarda, C. freundii, E. cloacae, E. aerogenes and the pathogenic Neisseriae. Essentially no activity against Serratia and Pseudomonas spp. was observed. Compared to the other cephalosporins tested, BL-S786 showed poor activity against staphylococci and streptococci. For most species tested, the MBC of the various cephalosporins was the same or within 1 dilution of their respective MIC. For Enterobacter and indole-positive Proteus spp., the MBC of BL-S786 and cefamandole was usually .gtoreq. 8-fold higher than MIC. Cefoxitin showed little MIC/MBC variations against indole-positive Proteus spp. Inoculum size had only a small effect on the MIC against most gram-negative species, in some instances > 64-fold increases in MIC resulted by increasing inoculum size from 105 to 107 organisms/ml.