Advisory for BAM Users on Reported Supply Problems for Cycloheximide

Cycloheximide (CH), a.k.a. actidione, is used in the Bacteriological Analytical Manual (Edition 8 Revision A, 1999, Chapter 10) for Listeria monocytogenes methodology to inhibit molds and yeasts (fungi). Shortages in the supply of this chemical have occurred unexpectedly. Remedies are suggested below. This advice will be updated as additional relevant technical information becomes available.

1. Continue using CH as long as available.
2. Reorder CH when possible from Sigma-Aldrich-Fluka, Oxoid (formerly Unipath), and other suppliers.
3. If all CH supplies are exhausted, the preferred substitute is pimaricin (natamycin) at 25 mg/L, which has been thoroughly studied [J. Food Protection 58: (11) 1263-1267 (1995)]. Pimaricin also appears to be safer for analysts than other anti-fungal compounds.
4. Alternate, less preferred, substitutes are the anti-fungal compounds amphotericin B or nystatin. There are not yet firm recommendations for final concentrations of these two compounds. Solubility will be a determining factor with these substitutes. Note than any selective agent has potential toxicity even for the selected analyte. There is no data on the toxicity of these compunds for Listeria.
5. One possibility, if you know or can determine that the matrices that you are testing are low in yeast and mold counts, is to do without an anti-fungal agent. This is, of course, inappropriate for mold ripened cheeses or smoked seafood. In any case, you should test a spiked matrix enrichment with and without CH before choosing to proceed without fungal inhibitors.
6. The above comments apply to the Listeria enrichment. For Listeria selective agars that use CH, e.g. Oxford agar, other CH-less alternatives are listed in the BAM's Listeria monocytogenes chapter. At least temporarily, MOX (Modified Oxford agar) may also be added to the list of selective agars (Note that the BAM uses two selective agars in parallel). The Oxford formulation without CH could also be used, with the caveat noted for a CH-less enrichment medium ,except if an anti-fungal is being used in the enrichment.
7. Further information on CH supply will be posted. Please e-mail or fax comments and questions to Anthony.Hitchins@cfsan.fda.gov [202-401-7740].

A.D.Hitchins.
2000-04-01

Hypertext updated by rim/kwg/cjm 2001-OCT-24