Comparison of methods for determining Escherichia coli concentrations in recreational waters

Seventy water samples were collected from three Lake Erie beaches to compare recoveries of Escherichia coli (E. coli) using the USEPA-recommended method for recreational waters (mTEC) to recoveries using three alternative methods (MI, modified mTEC, and Colilert). Statistical tests showed no differences in recoveries of E. coli between MI and mTEC; however, statistically-significant differences were found between modified mTEC or Colilert and mTEC. The MI agar method provided the most similar assessment of recreational water quality to mTEC among the three alternative methods tested. The range of differences between Colilert and mTEC was widest among the three alternative methods. In a sample group with a range of values near the single-sample bathing-water standard, recoveries of E. coli were statistically lower using modified mTEC than mTEC; however, MI and Colilert compared well to mTEC in this range. Because samples were collected in a small geographic area, more work is necessary to test within-method variability of the modified mTEC, MI, and Colilert methods and to evaluate these methods as substitutes for the mTEC method in a variety of recreational waters. Copyright (C) 2000.