Detection of Shoreline Fecal Contamination of a South Florida Beach using Traditional Indicator Organisms and a Novel Molecular Approach

Detection of Shoreline Fecal Contamination of a South Florida Beach using Traditional Indicator Organisms and a Novel Molecular Approach

Alvin Sherman Library 2053

The water quality of recreational bathing beaches in Florida is monitored by the Florida Department of Health who count the numbers of fecal indicator organisms in the water. This is necessary because considerable epidemiological research has shown that there are health risks associated with bathing in sewage-contaminated waters. Recently, the U.S. Environmental Protection Agency (EPA) in their 1999 Action Plan for Beaches and Recreational Waters recognized that the ‘swash’ zone of the beach may pose an increased health risk for children and other beach users. It was reasoned that sand may filter and accumulate fecal organisms and that the protective sites afforded by the high nutrient sand environment may increase the survival of fecal organisms. Ongoing research at the Oceanographic Center of NSU has shown that sand does indeed harbor higher numbers of fecal indicator organisms, although it is possible that these are ‘environmental strains’ adapted to life in sand. In short, their presence may not accurately reflect the degree of fecal contamination. The present study sampled a beach that is little used by bathers (i.e John U. Lloyd State Park Beach). The numbers of fecal indicators (E. coli, fecal coliforms, and enterococci) in the water and sand of this beach were enumerated and the counts were compared with available data for the nearby, heavily used, Hollywood Beach. Over a 4-month sampling period, numbers of indicator bacteria varied markedly, however, there were always more bacteria in the sand than in the water (around 5 fold). The numbers of bacteria at Hollywood beach were close to double the levels at John U. Lloyd Park beach. This suggests that the number of bathers influenced the fecal counts. While some of the bacteria may have come from bathers directly, it is likely that the effects were indirect. For example, the sloughing of skin cells from beach users may have added nutrients to the sand and subsequently increased the survival (and number) of indicator bacteria. The flushing out of these bacteria from the sand by wave action would have carried more bacteria into the water column. Therefore, this result suggests that counts in the water column at busy beaches may be elevated and consequently may be overestimating the levels of sewage contamination in the water. In an attempt to substantiate this conclusion, molecular methods were used to try to detect the human fecal bacterium Shigella in water and beach sand. Primers specific for a toxin gene in this bacterium were used. Any positive amplification would suggest that the Shigella were recent and from sewage since ‘environmental’ Shigella inhabiting the sand would be unlikely to retain this toxin gene. PCR amplifications of water samples and sand samples all failed to detect this Shigella on John U. Lloyd beach tentatively suggesting that the levels of indictors were not truly reflecting fecal contamination. At this time, the data is too preliminary for firm conclusions, however, it does show promise for using molecular methods in water quality assessment.