Two DRBC quality issues you should know.
This article may help you troubleshoot quality issues with the DRBC medium.
DRBC medium is described in ISO 21527-1 for the isolation and enumeration of yeast and moulds. DRBC is the abbreviation of Dichloran Rose-Bengal Chloramphenicol Agar. Rose-bengal photo-oxidizes to form toxic compounds. Store DRBC plates in the dark and avoid exposure to light. Some strains of moulds may be inhibited on this medium. Failure to properly store the DRBC plates may result in the following issues:
1. No growth of Saccharomyces cerevisiae
When quality control shows less growth on the DRBC plates than expected, it can happen that the DRBC plates have been in the light for too long. When DRBC is exposed to light, this will result in the formulation of inhibitory compounds. Therefore keep the DRBC media in the dark and cool place until used.
In particular, Saccharomyces cerevisiae will inhibit growth when DRBC plates are exposed to light for too long.
2. No sporulation of mould colonies
The mould colonies of CRM-PAUYL, a multistrain of mould and yeast, or CRM-PAU, a single mould strain, on DRBC, can vary from supplier to supplier. Sometimes sporulation hasn’t started yet. However, the yeast always shows the same appearance on de DRBC of different suppliers.
It is also possible that different colony forms can be observed in one lotnumber of DRBC while the plates have been inoculated simultaneously. For example, the first DRBC plate (#009) of a batch show sporulation after five days, while the later poured plate (#949) in the batch does not yet show sporulation.