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Dichloran-rose bengal medium for enumeration and isolation of molds from foods
Abstract:
Overgrowth by spreading molds such as Rhizopus and Mucor species is a problem with fungal enumeration media used for foods. Thirty-one antifungal compounds were surveyed for their ability to selectively inhibit such fungi while allowing growth of mycotoxigenic molds and other species of significance in food spoilage. Dichloran (2,6 dichloro-4-nitroaniline) restricted growth of Rhizopus stolonifer while allowing satisfactory growth of the other test molds. Three Rhizopus and Mucor species were encountered that were not inhibited by dichloran; these were controlled by the addition of rose bengal. The optimal medium, designated DRBC, contained 2 micrograms of dichloran and 25 micrograms of rose bengal per ml. DRBC, in pure culture tests and with food samples, restricted the colony size of spreading molds and recovered a wider range of species in higher numbers than other enumeration media.
Insights
This study introduces DRBC, a new fungal enumeration medium that effectively inhibits spreading molds like Rhizopus and Mucor. DRBC improves the recovery of significant food spoilage fungi in food samples.
Area of Science:
- Food microbiology
- Mycology
- Food safety
Background:
- Overgrowth by spreading molds (e.g., Rhizopus, Mucor) hinders accurate fungal enumeration in food.
- Existing fungal enumeration media face challenges in selectively inhibiting these molds while allowing beneficial fungi to grow.
Purpose of the Study:
- To identify antifungal compounds that selectively inhibit spreading molds.
- To develop an improved fungal enumeration medium for food analysis.
Main Methods:
- Surveyed 31 antifungal compounds for selective inhibition of spreading molds.
- Tested dichloran (2,6-dichloro-4-nitroaniline) and rose bengal for efficacy.
- Formulated and evaluated the optimal medium, designated DRBC, using pure cultures and food samples.
Main Results:
- Dichloran effectively inhibited Rhizopus stolonifer but not all Rhizopus and Mucor species.
- The addition of rose bengal to dichloran provided control over resistant mold species.
- The DRBC medium (2 µg/ml dichloran, 25 µg/ml rose bengal) restricted spreading mold colony size.
- DRBC demonstrated superior recovery of a wider range of fungal species in higher numbers compared to other media.
Conclusions:
- The DRBC medium is effective in controlling spreading molds in food samples.
- DRBC enhances the accuracy and scope of fungal enumeration in food microbiology.
- This medium improves the detection of significant food spoilage fungi.