Question:
In our project, we test the antifungal activity of some compounds against fungi as Candida or Malassezia.My question is about the medium. Could you tell me why the NCCLS decided to use RPMI 1640 as the test medium? The problem is I can’t grow the fungi in this medium. And, could you tell me why they propose to use RPMI 1640 lacking sodium bicarbonate? What occurs with sodium bicarbonate?
Answer:
The NCCLS methods are reference standards, not intended for routine use in clinical laboratory settings. Nonetheless, the procedures set forth in their documents provide a starting place for most ongoing research.
RPMI has been the medium for testing for almost 20 years now and was chosen as the standard after comparison with many other media in testing performed by several laboratories across the U.S.
Basically, the choice was decided on the basis of a need for a chemically defined, reliably prepared and commercially available medium. As used, the RPMI is buffered with MOPS (morpholinepropanesulfonic acid), which is probably the reason that sodium bicarbonate is not included.
Candida species grow well in this medium. Malassezia may require an oleic acid supplement (olive oil).
For additional information about the NCCLS antifungal susceptibility testing standards development, please see reference below:
Ghannoum MA, Rex JH, Galgiani JN. Susceptibility testing of fungi: current status of correlation of in vitro data with clinical outcome. J Clin Microbiol. 1996 Mar;34(3):489-95
Espinel-Ingroff A, Bartlett M, Bowden R, Chin NX, Cooper Jr C, Fothergill A, McGinnis MR, Menezes P, Messer SA, Nelson PW, Odds FC, Pasarell L, Peter J, Pfaller MA, Rex JH, Rinaldi MG, Shankland GS, Walsh TJ, Weitzman I. Multicenter evaluation of proposed standardized procedure for antifungal susceptibility testing of filamentous fungi. Journal of Clinical Microbiology, Jan 1997, 139-143, Vol 35, No. 1