The assessment of antimicrobial activity in an in-vitro model of the treatment of bacterial cystitis.

In order to investigate the comparative activity of agents of the nalidixic acid series, cultures of nalidixic acid sensitive strains of E. coli were exposed to the drugs in an in-vitro model that simulates the hydrokinetic aspects of the treatment of bacterial cystitis. Intrinsic activity, as judged by the response to a single dose of drug and resistance as judged by response to a repeat dose, were investigated. All seven compounds tested in this way were able to inhibit bacterial growth for considerable periods of time even when the peak concentration achieved was as low as 10 mg/l. However, resistance emerged readily, particularly to nalidixic acid, pipemidic acid and piromidic acid. Norfloxacin was the most active of the seven compounds tested and was the only one to which resistance did not emerge at the concentrations tested. However, when two nalidixic acid resistant strains were tested in the bladder model, norfloxacin resistance was observed to emerge with one strain, but not with the other.