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A total of 127 Gram-negative bacteria resistant to nalidixic acid were isolated from as many patients affected by urinary tract infections and hospitalized in the first Clinic of Infectious Diseases, University of Naples. Enterobacteria were identified by Enterotube system (Roche) and API 20 system (Ayerst). Non-fermentative bacteria were identified by OXI/FERM system (Roche). The following bacteria were collected: Escherichia coli 50, Proteus spp. 35, Enterobacter agglomerans 12, Serratia sp. 5, Pseudomonas aeruginosa 25. The in vitro antibacterial activity of nalidixic acid and three other quinoline derivatives (pipemidic acid, oxolinic acid and ciprofloxacin) were studied by determining the MICs by a miniaturized dilution broth method. The MICs were compared to evaluate the eventual cross resistance to the drugs under examination within each bacterial species. The results showed that 23% of bacteria were resistant to nalidixic acid, pipemidic acid and oxolinic acid; 49.6% to nalidixic and pipemidic acid and 0.7% to nalidixic acid and oxolinic acid. On the other hand none of the bacteria were resistant to ciprofloxacin. The last showed very low MICs against all the bacteria under examination, including Pseudomonas and Serratia. The high antibacterial activity of ciprofloxacin even against bacteria highly resistant to the other quinolines could be due to a greater affinity of the target sites or to the better permeability of resistant strains to the newer drug or because it is unaffected until now by mutations of genes responsible for cross resistance.

A total of 375 Gram-negative bacterial strains were isolated from midstream urine specimens of the same number of patients affected by urinary tract infections. All bacteria were identified by standard bacteriological methods and their susceptibility to six quinoline derivatives (ciprofloxacin, cinoxacin, norfloxacin, oxolinic acid, pipemidic acid, nalidixic acid) was studied by determining the MICs and MBCs for each compound using a miniaturized dilution broth method in microtitre plates and twofold dilutions of each drug from 256 to 0.12 mcg/ml. Ciprofloxacin, a new quinoline carboxylic acid compound structurally related to nalidixic acid, showed a much higher antibacterial activity against all bacterial strains under examination, including Pseudomonas, than the other compounds, except for norfloxacin. The MIC90 and MBC90 of ciprofloxacin never exceeded 1 mcg/ml with any of the bacterial species; and MBC/MIC ratios were very low, which represents an important clinical advantage. Only norfloxacin showed comparable effectiveness. No bacterial strain showed resistance to the drug and the MIC90 and MBC90 never exceeded 8 mcg/ml.

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.