Thymidine-dependent Escherichia coli infection and some associated laboratory problems

The rapid emergence of a thymidine-dependent strain of Escherichia coli in a patient treated with co-trimoxazole is described. The organism was recovered from blood cultures during a septicaemia which developed after only a few days of co-trimoxazole treatment. The cultural characteristics of three thymidine-dependent strains were studied and a remarkable variation was found in their ability to grow on different batches of blood agar, depending upon the age of the plates and the type of agar base used.