Thymine-requiring bacteria associated with co-trimoxazole therapy.

Since 1971 thymine-requiring (thy-) pathogens have been isolated from the urine of 8 patients with renal calculi, and from the sputum of 1 patient with chronic chest infection. The patients had been treated with co-trimoxazole for several months before the isolation of the mutant pathogens. There was persistent pyuria in the patients with renal calculi, and purulent sputum in the patient with chronic chest infection. The mutants were identified by their inability to grow on diagnostic sensitivity test agar (D.S.T., Oxoid) which is deficient in thymine. It was found that wild-type bacteria can produce growth factors for the metabolism of the mutants in vitro, and the urine of the patients contained by thymine-like compounds. These findings indicate that thy- mutants may develop in renal calculi during co-trimoxazole therapy. Therapy should be changed to a more suitable antimicrobial as soon as possible after diagnosis of mutant infection.