ular emphasis on methods for specific detection of Escherichia coli. DETECTION OF ENZYMATIC ACTIVITIES General Considerations Three groups of fluorogenic and/or chromogenic reactions have been used. (i) The first is hydrolysis of synthetic substrates by bacterial enzymes, causing considerable increase in the fluorescence and/or absorption of the bacterium-substrate mixture (16). Fluorogenic synthetic enzyme substrates containing coumarin derivatives of 4-methylumbelliferone (4-MU) or 7-amino-4-methylcoumarin (7-AMC) are the most commonly used substrates. This popularity could be ascribed to availability of a wide range of substrates with different metabolic moieties, noncarcinogenicity, ease of visual detection of the 335

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CHROMagar Candida is a new differential culture medium that allows selective isolation of yeasts and simultaneously identifies colonies of Candida albicans, Candida glabrata, Candida tropicalis and Candida krusei. We evaluated this medium and compared it with a reference medium, Sabouraud glucose agar, for the presumptive identification of yeast species isolated directly on the medium from 1150 clinical specimens. A total of 731 specimens showed no growth, 299 isolates (70.2%) showed growth to the same extent on both media. Forty mixed cultures were detected on both media. More than one isolate was detected in 30 of the tested specimens on either CHROMagar (26 specimens) or Sabouraud glucose agar (four specimens). We found a sensitivity of 98.8% and a specificity of 100% for C. albicans, 66.7% and 99.8% for C. tropicalis, 100% and 100% for C. krusei, and 98% and 95.7% for C. glabrata. Regarding these results, CHROMagar Candida is recommended as a useful isolation medium capable of the presumptive identification of yeasts and better detection of mixed cultures in clinical specimens.