In-vitro antibacterial activity of DQ-2556 and its stability to various beta-lactamases

DQ-2556, a new cephalosporin, showed a broad antibacterial spectrum over Gram-positive and -negative organisms. The activity of DQ-2556 against recent clinical isolates of Gram-positive cocci and Enterobacteriaceae was comparable with that of cefpirome, and superior to that of ceftazidime. DQ-2556 was almost as active as cefpirome against Pseudomonas aeruginosa, but was less active than ceftazidime. With the exception of Ps. aeruginosa, DQ-2556 was bactericidal against various organisms at either the MIC or twice the MIC. DQ-2556 bound preferentially to penicillin-binding proteins (PBPs) 2, 1 and 3 of Staphylococcus aureus, PBPs 3, 1A and 1B of Escherichia coli and PBPs 1A, 3 and 4 of Ps. aeruginosa. DQ-2556 was stable to various penicillinases and cephalosporinases, but was unstable to oxyiminocephalosporinases. The Km values of DQ-2556 for the cephalosporinases of Citrobacter freundii and Enterobacter cloacae were only two- or three-fold higher than those of ceftazidime, indicating that DQ-2556 had a relatively high affinity for these enzymes compared with other recently developed cephalosporins. The MIC of DQ-2556 for Esch. coli increased four-fold in an OmpF-deficient mutant, indicating that the OmpF porin was one of the major routes for penetration of DQ-2556 into Esch. coli cells.