Attempted reversal of oxytetracycline resistance of Proteus mirabilis by EDTA-tromethamine lavage in experimentally induced canine and feline cystitis.

An attempt was made to reverse the antibiotic resistance of Proteus mirabilis used to induce experimental cystitis in cats and dogs. Results of in vitro studies on an oxytetracycline-resistant strain of P mirabilis, utilizing standard plate counts, indicated the organism became susceptible to oxytetracycline when it was treated with a solution of EDTA-tromethamine. In vivo experiments were conducted with cats and dogs in which 50% of the experimentally infected animals were treated with bladder lavage twice daily with EDTA-tromethamine solution and 50% with tromethamine buffer alone; all were given standard doses of oxytetracycline. Results of bacteriologic cultural examinations of urinary samples and urinalyses done each day, at the end of the experiments, indicated all animals had cystitis. Thus, although the organism's resistance to oxytetracycline was changed by EDTA-tromethamine in vitro, change in bacterial resistance did not occur in vivo in cats and dogs during clinical treatment.