Macroscopic detection
Fungi and mold can appear as small isolated colonies of grey, white or greenish color, floating at the surface of the medium. It is important to inspect the culture vessel with the naked eye and look for colonies which rest on the medium surface and will be missed during microscopic inspection. If the contamination is substantial, the medium will become turbid and cloudy, and spots on the vessel surface may appear. Sometimes fungal contaminations will cause a pH increase of the medium, resulting in phenol-red containing media to appear pink.