Antibacterial activity of six beta-lactams and six quinolones against urinary gram negative bacteria

Three hundred eighty seven gram negative bacterial strains were isolated from urine specimens of as many patients affected by urinary tract infections. Susceptibility of bacteria to six quinolones (ciprofloxacin, norfloxacin, oxolinic, nalidixic, pipemidic acid and cinoxacin) and six beta-lactams (ceftazidime, ceftizoxime, ceftriaxone, cefamandole, cefoxitin and cefotaxime) was studied determining the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of each compound by a miniaturized dilution broth method. Ciprofloxacin, a quinoline carboxylic acid compound structurally related to nalidixic acid, and ceftazidime a new beta-lactamase stable beta-lactam showed a much higher antibacterial activity against all the bacterial strains including Pseudomonas. The best antibacterial activity of ciprofloxacin and ceftazidime was expressed either by the lower MICs and lower MBCs with respect to those of the other compounds or by a low MBC/MIC ratio, which represent an important clinical advantage in clinical practice.