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Comparison of the Multiple-sample means with composite sample results for fecal indicator bacteria by quantitative PCR and culture
Citation:
Converse, R., L. Wymer, A. Dufour, AND Tim Wade. Comparison of the Multiple-sample means with composite sample results for fecal indicator bacteria by quantitative PCR and culture. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. American Society for Microbiology, Washington, DC, 78(19):7166-69, (2012).
Impact/Purpose:
The purpose of this study was to determine whether composite sampling gave statistically similar results to multiple-point sampling when QPCR is used to measure bacterial water quality and whether the two sampling strategies are likely to produce the same beach closure decisions.
Description:
ABSTRACT: Few studies have addressed the efficacy of composite sampling for measurement of indicator bacteria by QPCR. In this study, composite results were compared to single sample results for culture- and QPCR-based water quality monitoring. Composite results for both methods were similarly-correlated to multiple sample means and predicted criteria exceedances equally. Because fecal indicator bacteria (FIB) concentrations can be variable within a beach area, several water samples from a beach may be required to sufficiently characterize water quality (15). Due to the cost of the analysis of multiple samples, analyzing composited samples may be a reasonable and less expensive alternative (9). Compositing involves mixing equal volumes of spatially discrete samples and analyzing the homogenate. In enumeration of FIB by culture-based methods in water samples, composite sample results have been shown to be significantly correlated to the arithmetic means of single samples results and to yield similar beach closure decisions (1, 6, 8). Moreover, analysis of a single composite sample can be nearly 40% cheaper than multiple single sample culture analyses (8). Recent studies have suggested that rapid water quality testing methods such as quantitative polymerase chain reaction (QPCR)are statistically associated with gastrointestinal illness among swimmers (12, 13, 14) , and composite sampling could generate significant savings for water quality monitoring programs using QPCR. Because the empirical relationships between culture and QPCR results can vary within a beach on small temporal and spatial scales (3), it is unclear whether composite sampling is as efficacious when using QPCR as when using culture methods. The purpose of this study was to determine whether composite sampling gave statistically similar results to multiple-point sampling when QPCR is used to measure bacterial water quality and whether the two sampling strategies are likely to produce the same beach closure decisions.