Quality control of two rose bengal and modified DRBC and DG18 media

The effect of storage on the performance of four mycological media, DG18, DRBC and two Rose Bengal agars, one from Difco, the other recommended by the Swedish Standard Institution, was investigated. The autoclaved media were stored (+4 degrees C) in the dark for up to 26 weeks. Following each storage period, the media were remelted and poured and the plates stored (+4 degrees C) in the dark for a maximum of 8 weeks before inoculation with test microorganisms. All media contained antibiotics. Both rapidly and slowly growing moulds, and also yeasts and bacteria were used as test microorganisms. No distinct effect of storage time on colony appearance could be shown for any of the four media. If the loss of restricted growth of Rhizopus stolonifer is used as a measure of the performance of the media, DRBC plates should not be stored for longer than 2 weeks after being poured from fresh medium. Storage of DRBC in flasks should not exceed 4 weeks and plates prepared from this medium should not be kept for more than 1 week. DG18 plates should only be poured from fresh medium and kept for a maximum of 1 week. The inhibitory effect of the antibiotic supplement on bacteria lasted for at least 4 weeks in DG18 and the two rose bengal media.