Inhibitory and bactericidal activity of cefmetazole and seven other beta-lactams against different bacterial inocula

The determination of the minimal inhibitory concentrations (MICs) at different bacterial inocula represents an important factor in determining the potential effectiveness of new antibiotics. MICs at different inocula (10(5) and 10(7) CFU/ml) and minimal bactericidal concentrations (MBC) of cefmetazole and seven other new cephalosporins (ceftazidime, ceftizoxime, cefamandole, ceftriaxone, cefotaxime, cefuroxime, cefoxitin) were determined by a miniaturized dilution broth method against a wide range of gram-positive, gram-negative and non-fermentative bacteria. The results of the present investigation confirm that all the beta-lactams under examination including cefmetazole exert a good or satisfactory antibacterial activity against gram-positive and gram-negative bacteria; and that only ceftazidime possesses antipseudomonas activity. MBCs and MICs at heavy inoculum are two times higher than MICs at light inoculum. These results could explain the spread by different mechanisms of bacteria resistant to beta-lactam antibiotics.