Prevalence of yeasts in beach sand at three bathing beaches in South Florida
Introduction
The occurrence and activity of yeasts in near-shore marine waters is well established (Meyers and Ahearn, 1974; Kohlmeyer and Kohlmeyer, 1979) due to their role in the decomposition of organic substrates, nutrient recycling, biodegradation of hydrocarbons, and as prey for a variety of marine organisms (Siepmann and Hoehnk, 1962; Meyers and Ahearn, 1974; Lachance et al., 1976). More recently, there has been an interest in yeast populations inhabiting recreational beaches, particularly those concerned with human health. Papadakis et al. (1997) found a positive correlation between the numbers of swimmers and the presence of yeasts of human origin. Increasingly, it is being realized that traditional fecal indicator organisms, such as enterococci, can be poor measures of bathing water quality and the inclusion of non-traditional indicators, such as yeasts, may be desirable when testing recreational waters (Papadakis et al., 1997).
Open-ocean waters can contain between 10 and 100 yeast cells per liter, while near-shore waters support much larger populations, i.e. up to several thousand cells per liter (Fell, 1976), because these waters receive significant input from terrestrial yeasts (van Uden and Fell, 1968) and sewage-derived yeasts (Cooke et al., 1960; Fell, 1976). Fell et al. (1960) contend that in estuarine regions the majority of yeast species are of non-marine origin. In Biscayne Bay, Florida, Fell and van Uden (1963) demonstrated that population densities of intestinal yeasts often fluctuated according to the degree of pollution.
Beach sand receives constant microbiological inputs from the water, through the filtering action during tidal cycles, and from washout from land during rain events. Beach users also contribute directly to the microbial quality of beach sand. Consequently, recreational beaches may harbor significant yeast populations, particularly, if sand particles provide a micro-habitat for the enhanced survival of yeasts as suggested by Ghinsberg et al. (1994). Sand might be an important reservoir of yeasts and afford a health risk for beach users (Papadakis et al., 1997), since some 150 yeast species are pathogenic to humans and animals (Kwon-Chung and Bennett, 1992). Candida spp. infections, in particular, have increased dramatically in recent years due to the increase in immunocompromised individuals in the population (Cooke et al., 2002).
A few prior studies have demonstrated the presence of yeasts in sand. For example, Kishimoto and Baker (1969) found dermatophytes to be common in beach sands in Hawaii and Papadakis et al. (1997) isolated yeasts from water and sand samples collected from a bathing beach in Greece. At least one study isolated human pathogenic fungi from beach sand (Anderson, 1979), while another reported pathogenic species from coastal areas of California (Dabrowa et al., 1964). However, the present study is the first to document the nature and abundance of yeast populations in subtropical beach sands.
It was therefore, the purpose of this study, to identify and enumerate the yeast species, which inhabit the sediments at three bathing beaches to determine if yeast species may have value as indicator organisms and to gain insight in the ecology of yeasts in subtropical intertidal environments.
Section snippets
Sampling
Sand samples were collected from three recreational beaches in South Florida between August 2001 and July 2002. Hobie Beach in Miami (25°44′22.5′′N, 80°10′18.7′′W) represented a ‘heavy use’ beach because of the high density of users per unit area. Fort Lauderdale (26°07′17.35′′N, 80°06′14.24′′W) represented a ‘moderate use’ beach and Hollywood Beach (26°02′02.56′′N, 80°06′50.36′′W) was a ‘light use’ beach. At each beach, two transects (100 m apart) running perpendicular to the water line were
Results
Hobie Beach sand in Miami had the highest counts of yeasts throughout the year (averaging 19,786 CFU 100 g−1 sand), regardless of sand type [wet or dry]) followed by Fort Lauderdale beach (2418 CFU 100 g−1 sand) and Hollywood beach (1715 CFU 100 g−1 sand). Hobie Beach, the most populated of the beaches studied, had significantly more yeasts (p<0.001) than the two other less populated beaches. Comparing the numbers of yeasts in the dry and wet sand for all three beaches, dry sand harbored significantly
Discussion
This study is the first to provide quantitative data showing high levels of yeast populations surviving in sub-tropical beach sands. Kishimoto and Baker (1969) and Papadakis et al. (1997), reported on the occurrence of yeasts in beach sand but these studies provided no information on the abundance of the populations. In a study of yeasts in the waters off Hobie Beach, Miami, Ahearn et al. (1968) reported yeast populations ranging from ca. 500 to 1000 cells per 100 ml. Although these abundances
Conclusions
More populated recreational beaches harbor greater numbers and species of potentially pathogenic yeast organisms.
High concentrations of yeast species may pose a health risk to human populations.
Selected yeast species such as C. albicans and C. tropicalis, may be useful, measurable indicators of the health risk associated with pollution and/or health risk of recreational beaches.
Acknowledgments
This work was partially funded by the United States Environmental Protection Agency (Grant R828830) to AR. The research results have not been subjected, however, to the EPA's required peer review and therefore do not necessarily reflect the view of the Agency. No official endorsement should be inferred. Participation by RSMAS (AT & JF) was funded, in part, by the NSF-NIEHS Oceans and Human Health Centers Program (NSF 0432368 and NIEHS P50ES12736).
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