Comparison of the ColiPlate™ Kit with Two Common E. coli Enumeration Methods for Water

Abstract

Quantitatively assessing fecal indicator bacteria in drinking water from limited resource settings (e.g., disasters, remote areas) can inform public health strategies for reducing waterborne illnesses. This study aimed to compare two common approaches for quantifying Escherichia coli (E. coli) density in natural water versus the ColiPlate™ kit approach. For comparing methods, 41 field samples from natural water sources in Kentucky (USA) were collected. E. coli densities were then determined by (1) membrane filtration in conjunction with modified membrane-thermotolerant E. coli (mTEC) agar, (2) Idexx Quanti-Tray® 2000 with the Colilert® substrate, and (3) the Bluewater Biosciences ColiPlate kit. Significant correlations were observed between E. coli density data for all three methods (p < 0.001). Paired t-test results showed no difference in E. coli densities determined by all the methods (p > 0.05). Upon assigning modified mTEC as the reference method for determining the World Health Organization-assigned “very high-risk” levels of fecal contamination (>100 E. coli CFU/100 mL), both ColiPlate and Colilert exhibited excellent discrimination for screening very high-risk levels according to the area under the receiver operating characteristic curve (~89%). These data suggest ColiPlate continues to be an effective monitoring tool for quantifying E. coli density and characterizing fecal contamination risks from water.