Pre-enrichment and enrichment. Incubate for 4 h at 30° C, add the selective agents and continue incubating for a total time of 48 h at 30° C. If cycloheximide is unavailable, the preferred substitute is pimaricin (natamycin) at 25 mg/L (27). Natamycin is much safer to use than cycloheximide. Another possibility, if the matrices of interest (e.g. pasteurized milk and cream, yogurt, and precooked frozen seafood) are low in yeast and mold, is to do without an anti-fungal agent. This is not advisable for mold-ripened cheeses, smoked or dried seafood or fresh produce.