Holding-time and method comparisons for the analysis of fecal-indicator bacteria in groundwater

Abstract

As part of the US Geological Survey National Water-Quality Assessment Program, groundwater samples from domestic- and public-supply wells were collected and analyzed for fecal-indicator bacteria. A holding time comparison for total coliforms, Escherichia coli, and enterococci was done by analyzing samples within 8 h using presence/absence methods and within 18-30 h using quantitative methods. The data indicate that results obtained within 18-30 h were not significantly different from those obtained within 8 h for total coliforms and enterococci, by Colilert® and Enterolert® methods (IDEXX Laboratories Inc., Westbrook, ME), respectively. Quantitative laboratory methods for samples analyzed within 18-30 h showed a statistically significant higher detection frequency when compared to presence/absence methods done within 8 h for the following methods, E. coli by Colilert and enterococci by membrane filtration on mEI agar. Additionally, a comparison of methods for the enumeration of enterococci was done. Using non-parametric statistical analyses, results from the two methods were statistically different. In this study, the membrane filtration method on mEI agar was more sensitive, resulted in more detections of enterococci, and results were easier to interpret than with the quantitative Enterolert method. The quantitative Enterolert method produced varying levels of fluorescence, which required additional verification steps to eliminate false-positive results. It may be more advantageous to analyze untreated groundwater for enterococci using the membrane filtration method on mEI agar.

Extending the Holding Time for Agricultural Water Testing EPA Method 1603 for Produce Growers

“…The study also supported the conclusion that sample storage could be extended to 24 h for analysis of microorganisms without altering the mean levels of E. coli, which is in accordance with the results of this paper. Another similar study [21] supported the results reported in this study, stating that extending sample holding time from 8 to 30 h does not affect the bacterial population and also mentioned the possibility to extend sample storage time to 62 h [22]. Extending sampling holding period promotes water testing by making it easier to access certified laboratories in the region through overnight shipment, coordination of delivery with other growers, or transporting by self.…”

Monitoring Approaches for Faecal Indicator Bacteria in Water: Visioning a Remote Real-Time Sensor for E. coli and Enterococci

“…Enzyme activity assays [7,22,26,28,[42][43][44]77,82,[99][100][101][102][103][144][145][146][147][148][149][150] The assays use enzyme chemistry and are used within biosensors and find results through fluorescence. Additionally, used in portable field kits, automated instruments, and traditional laboratory techniques.…”

“…These processes required filtration, selective media, defined substrate technology, and specific reagents. Bushon et al [101] performed a holding time comparison for Colilert and Enterolert by analysing samples within 8 h using presence and absence detection methods and within 18-30 h using quantitative methods. They determined that the results for the Enterolert method was not significantly different; however, for Colilert, the quantitative laboratory methods for samples analysed within 18-30 h showed a statistically significantly higher detection frequency than the presence and absence detection method for analysis within 8 h. They identified that result times were at a minimum within 8 h but Colilert had better results within 18-30 h; and that both methods required multiple processing steps, which limited the efficiency [101].…”

“…Membrane-filtration assays [7,8,22,[26][27][28][29][30][31][32][33][34]101] Widely used standard reference methods to identify bacteria, virus, and organisms. Membrane filtration verifies, compares, and references water tests by isolating and eliminating discrete microbiological colonies for multiple samples and volumes.…”