Isolation and Identification of Yeasts from the Barren River

The Barren River was sampled twice monthly for one year to obtain data on aquatic yeasts. Sites upstream and downstream of the Bowling Green sewage plant, as well as the sewage effluent, were sampled to ascertain if the effluent had any effect on the yeast population of the river. Sporadic yeast counts were obtained which averaged 40 CFU/ml for the effluent, while the river averaged 15 CFU/ml. A total of 318 yeasts were isolated and identified during the study, including 16 different genera with Cryptococcus being the most common. Cryptococcus laurentii occurred most frequently of the 67 different species identified. The sewage effluent was not found to contribute significantly, either in number or in particular species, to the river yeast flora, although the effluent flora differed from the yeast flora in the river. Statistical analysis suggested relationships between yeast counts and several environmental parameters, particularly chlorine, turbidity, nitrate and phosphate levels. Some yeast pathogens of low virulence were isolated, but the probability of the river being a vector of mycotic disease was not found to be great. No seasonal variation was noted in yeast counts. The pathogenic yeast, Candida albicans, was not isolated. Two commercial yeast identification systems were tested. Neither system could be recommended for identifying aquatic yeasts