Response of ampicillin resistant Escherichia coli to cephalosporins in an in vitro model simulating conditions of bacterial growth in the urinary bladder.

Five ampicillin resistant strains of Escherichia coli were exposed to cephalosporins in an in vitro model which simulates the hydrokinetic features of the urinary bladder. Although the strains showed substantial zones of inhibition when tested against cephalosporins by the disc diffusion method, the results in the bladder model suggest that, in conditions where the antibiotic concentration is being reduced by dilution and micturition as well as enzymic hydrolysis by the organism, activity of this group of agents may be insufficient to eradicate infection. It is suggested that the results warrant a closer investigation into the efficacy of cephalosporins against ampicillin resistant Gram negative bacilli in vivo.