[Timed bacteriostatic and bactericidal activities of cefmetazole against selected gram-negative bacteria]

Antibacterial activities of cefmetazole, a new preparation of cephamycin antibiotic, were determined against selected clinical strains of Escherichia coli (27 strains), Klebsiella sp. (27 strains) and Bacteroides fragilis (27 strains). Activities were evaluated at bacteriostatic and also bactericidal levels with particular reference to time of exposure of microbes to the drug. The minimal drug concentrations producing minimal reduction of colony-forming units at time intervals of 3, 6 and 24 hours after exposure to the drug--approximations to the theoretical bacteriostatic concentrations--were designated as 3-h, 6-h and 24-h MRCs, respectively. Conventional MIC yielding no turbidity after incubation of antibiotic-containing broth for 24 hours was also determined. The minimal concentrations of the drug producing 99.9% killing at time intervals of 3, 6 and 24 hours after exposure to the drug were designated as 3-h, 6-h and 24-h MLCs, respectively. Assuming that the apparent mode of action of a drug is bactericidal when the ratio of bactericidal-bacteriostatic concentrations is low (less than or equal to 4) and bacteriostatic when high (greater than or equal to 8), then cefmetazole appeared to be a bactericidal drug to a considerable number of Gram-negative strains when the exposure time exceeded a period of 6 hours. The data that the mode of action of this drug is bactericidal with such relatively brief exposure times--indicating rapid decrease of colony-forming units--would suggest cefmetazole is an excellent antibacterial agent and would be a useful drug in treatment of bacterial infections.