Occurrence of gram negative bacteria in midstream bladder urine and their sensitivity to quinoline derivatives

326 gram negative bacteria have been isolated and quantitative bacteria counts performed from midstream urine of as many patients affected with symptomatic and non symptomatic urinary tract infections. Susceptibility of bacteria to four quinoline derivatives (Norfloxacin, Oxolinic acid, Pipemidic acid and Nalidixic acid) was studied determining the minimal inhibitory concentrations (MICs) of each drug by a miniaturized dilution broth method. The frequency of bacterial species isolated, the frequency of symptoms and the frequency of bacterial counts were studied to establish a possible relationship between these data. It has been observed that patients affected with pyuria without any other subjective symptoms demonstrate a colony count ranging between less than 10(4) and greater than 10(5) bacterial/ml of urine and these bacteriuria were determined by several different bacterial species. E. coli was much more frequently responsible for low or high count bacterial infections of the urinary tract than other species. In fact E. coli was detected in 64.4% of patients, P. mirabilis in 15.9%, E. agglomerans in 5.2%, P. aeruginosa in 4.9. Other species were detected in much lower percentages. Norfloxacin proved to be the most effective drug in vitro, out of those under examination. Its MIC50 never exceeded 8 mcg/ml even against Pseudomonas and Serratia strains, which were resistant to all the other antimicrobial agents.