Trimethoprim antagonists: effect of uridine in laboratory media

Abstract

Uridine prevents the uptake of thymine by thymineless mutants and strains rendered phenotypically thymineless by the presence of trimethoprim. The effect of adding uridine to various laboratory media was examined to determine whether its presence improved the media for trimethoprim sensitivity tests. Three of the media, Difco Mueller Hinton Agar, Oxoid Isosensitest Agar and Wellcotest Sensitivity Test Agar seemed to lack any thymine derivative and thus the presence of uridine did not affect their performance. Despite these findings, it seemed that they already contained added uridine. Two media, Oxoid Tryptone Soya Broth and Mueller Hinton Agar, were rendered suitable for trimethoprim sensitivity testing by the addition of uridine.