Incidence of thymidine-dependent enterococci detected on Mueller-Hinton agar with low thymidine content

It was observed that 10% of urine culture isolates of enterococci tested for antimicrobial susceptibility failed to grow on commercially prepared Mueller-Hinton agar with low levels of thymidine and thymine. All strains could utilize exogenous thymidine and thymine and required only low levels (0.4-microgram disk) to support growth. All thymidine-thymine-requiring strains were resistant to trimethoprim-sulfamethoxazole.