Development and evaluation of a selective medium for an anaerobe associated with non-gonococcal urethritis

The purpose of the study was to develop a selective medium for the isolation of an anaerobe that is associated with non-gonococcal urethritis. This was achieved by determining the sensitivity of 64 strains of the NGU-associated anaerobe to 20 antibiotics and three dyes by the disc-diffusion method. Then the MIC of eight of these antimicrobial agents for ten of the strains was determined by a tube dilution method. The results led to the formulation of a selective agar medium based on the incorporation of polymyxin (0.15 IU/ml), trimethoprim (10 micrograms/ml), vancomycin (10 micrograms/ml) and methyl green (32 micrograms/ml). This medium supported growth of the NGU-associated anaerobe but did not support growth of the other anaerobes tested. The selective nature of the medium made possible the recovery of the NGU-associated anaerobe from 13 of the 25 specimens from men with NGU, compared with isolation from only 8 of these men when using a non-selective medium.