Trimethoprim activity in media selective for Campylobacter jejuni.

The activity of trimethoprim (TMP) in two selective media used for isolation of Campylobacter jejuni was evaluated. The two selective media, Campy-BAP and Skirrow medium, contain TMP in addition to other antimicrobial agents. The minimal inhibitory concentrations of TMP in blood agar base (basal agar for Skirrow medium) or brucella agar (basal agar for Campy-BAP) for three sensitive control organisms were compared with those in Mueller-Hinton agar, which contains low levels of thymidine. TMP was inactive in both blood agar base and brucella agar, even when lysed horse blood or thymidine phosphorylase was added. TMP had activity when used in combination with the other antimicrobial agents normally included in Skirrow medium and Campy-BAP, probably indicating synergism between TMP and one or more of the other antimicrobial agents. Sheep blood could be substituted for lysed horse blood in Skirrow medium without compromising the activity of TMP.