Hi there,

Make sure your media is properly sterilized.

Make sure your inoculum is pure (ie.containing only the strain you intend to culture).

Make sure you work sterile.

To eliminate contaminants, streak the contaminated culture on plate in order to get isolated clones and then start from this for a new culture.

Hi @ Dominique Liger , thank you for your recommandations,

generaly i work under MSC Class II , media is sterilized by autoclav at 120°c/15 min

i think that the problem is my incoculum "traditional fermented wheat", wich naturaly contain yeast , lactic acid bacteria fungi and mold. so can i make YEPD media selective ? by adding somthing that stop mold but not yeast ?

The oxide method http://www.oxoid.com/UK/blue/prod_detail/prod_detail.asp?pr=CM0920&org=149&c=UK&lang=EN states states "Detection and enumeration of yeasts in the presence of moulds may be made easier by using a combined anaerobic/aerobic incubation procedure. Cultures are initially incubated for 3 days under anaerobic conditions and then for a further 2 days aerobically. Development of mould colonies is impeded during the anaerobic phase of incubation. Dimorphic moulds e.g. mucor spp may form yeast- like colonies during anaerobic incubation. It might be worth a try

thank you very much @Karen Hunt for this tip, this method work very well !