A membrane filter procedure is described for the enumeration of Candida albicans in natural waters. Several hundred milliliters of sample can be examined by filtration through 1.2-,um membranes. Selectivity is achieved by the use of a defined (yeast-nitrogen base plus maltose) agar medium, inclusion of the antimicrobial agents chloramphenicol and cycloheximide, and incubation at 370C. C. albicans colonies are differentiated primarily through color by use of a bismuth salt indicator system. Average recovery of various strains of C. albicans stressed in seawater at 40C was 82%, compared with those of spread plate controls on a noninhibitory medium. With river water and raw sewage, 90% of typical C. albicans colonies were confirmed as such in a simplified germ tube test. Atypical colonies verified as C. albicans were infrequent (3%). C. tropicalis and Torulopsis candida were the most common false-positive colonies.

Candida parapsilosis, C. tropicalis, and Torulopsis glabrata were the human-associated yeasts most frequently isolated from quahogs, oysters, and mussels collected from four estuarine areas along the northern shore of Long Island Sound. Some inconsistency and seasonal variation in the occurrence of these and other yeast species were noted. In particular, C. albicans densities were greatest during colder months in the more heavily polluted waters. A total of 347 yeasts were isolated and cultured at 37°C and, of these, 219 or 62% were human-associated forms. Generally, these yeasts in the animals sampled reflected the overall pollution status of the estuary from which they were taken. This study represents a clear demonstration of potentially pathogenic yeasts in a valuable marine resource. The occurrence of human pathogenic microorganisms in native populations of bivalve molluscs is well-documented (4-6, 9, 14, 20, 25, 27, 35, 37-39, 42). In addition, a variety of shellfish species have been shown to accumulate and eliminate coliforms (10, 11, 24), other bacteria (26), and virtlses (15, 30) under experimental conditions. These reports, in addition to outbreaks of viral hepatitis traced to the consumption of raw shellfish (7), indicate that recreationally and economically valuable bivalve molluscs represent a potential health hazard in some areas. Considering the filtering capacities of molluscan shellfish for particles in the yeast cell size range (23) and the known presence and survival of human pathogenic yeasts in coastal