Question

If you want to develop a growth medium that selects for the growth of fungi, and deters the growth of bacteria, would you make this medium neutral, acidic, or alkaline? explain your answer. What oxygen requirement would you expect from an organism that grows throughout a soft agar deep, with more growth at the surface than at the bottom? Give an example of a genus of a bacteria that has the previously mentioned oxygen requirement.

Answer 1

Answer 1:

Most fungi are acidophilic and grow well in acidic pH. pH value between 5 - 6 seems to support better fungal growth and inhibits most bacteria from growing. At the same time fungi can not tolerate high pH. In alkaline side pH above 8.0 will not be tolerated by most fungi.
Hence, in order to make a medium suitable for fungi and one that inhibits bacteria, an acidic pH is most ideal. Example: Sabraoud's agar is adjusted at pH 5.6

Answer 2:

With respect to oxygen requirements, the bacteria could be aerobic/anaerobic / facultative or microaerophilic.

The kind of growth pattern in which the growth is seen throughout the soft agar deep but the maximum growth is at the top of the tube, is shown by facultative bacteria. These bacteria grow best in presence of air but absence of oxygen is not detrimental to them and they can still grow well in such a condition. for Example: Escherichia coli, Staphylococcus aureus, Salmonella spp.