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COMPARISON OF ENTEROCCOCUS DENSITIES DETERMINED BY CULTURE AND QPCR ANALYSES IN WATER SAMPLES FROM TWO RECREATION BEACHES
Citation:
Haugland, R A., S D. Siefring, L J. Wymer, K Brenner, AND A P. Dufour. COMPARISON OF ENTEROCCOCUS DENSITIES DETERMINED BY CULTURE AND QPCR ANALYSES IN WATER SAMPLES FROM TWO RECREATION BEACHES. Presented at New England Association of Environmental Biologists (NEAEB), Hancock, MA, March 17-19, 2004.
Impact/Purpose:
The goal of this research project is to evaluate and compare methods that rapidly (less than 2 hours) measure fecal contamination of water with respect to accuracy, specificity, and ease of use.
Description:
Previous studies conducted by the U.S. Environmental Protection Agency (USEPA) have demonstrated that cell densities of the bacterial genus Enterococcus in water samples are directly correlated with gastroenteritis illness rates in swimmers at both marine and fresh water beaches. Based on these data, guidance has been proposed that unacceptable health risks may be associated with swimming in waters containing concentrations of these organisms in excess of per 104 colony forming units (CFU)/100 ml, as determined from one-time measurements. An improved, selective culture method (mEI agar membrane filter method) has been developed by the U.S. EPA for measuring Enterococcus concentrations in recreational water samples, however, this method still requires at least 24 hours to obtain results and, hence, may not allow timely notification of potential hazards to bathers. The U.S. EPA has initiated a new recreational water health study to evaluate the correlation between illness rates in swimmers and fecal indicator concentrations, determined by the mEI agar membrane filter method and several new technologies providing near real-time results. One of the new technologies being evaluated is quantitative polymerase chain reaction (QPCR) analysis.
Water samples from two Great Lakes freshwater beaches were collected three times daily on weekends during the summer of 2003. Samples were collected at beach 1 (West Beach, Indiana Dunes National Lakeshore) over a 10 week period and at beach 2 (Huntington Beach, Bay Village, Ohio) over an 8 week period. Totals of 336 and 420 samples were analyzed at beach 1 and beach 2, respectively. Preliminary analyses of the data have shown that Enterococcus concentrations at beach 1 ranged from <1 to 3.7 x 103 CFU/100 ml, as determined by the mEI agar filter method, and from non-detectable to 1.7 x 104 cells/100 ml, as determined by the QPCR method. Enterococcus concentrations at beach 2 ranged from <1 to 4.8 x 104 CFU/100 ml by the filter method and from non-detectable to 1.3 x 105 cells/100 ml by the QPCR method. The extrapolated detection limit of the QPCR method averaged 1 cell/100 ml water sample using 45 amplification cycles. Overall correlation factors, determined by regression analysis, for the log-transformed results of the two methods were 0.41 at beach 1 and 0.59 at beach 2. Of all the individual samples from both beaches, 17% contained Enterococcus concentrations > 104 CFU/100 ml, and of these, 95% also contained > 104 cells/100 ml determined by QPCR analysis. Determinations of correlations between illness rates in swimmers and Enterococcus measurements by the two methods are ongoing.