Comparison of Different Enumeration Protocols for Indicator Microorganisms in Water and Sediment

Introduction: Water quality, such as irrigation water quality, becomes more and more important for food safety. Escherichia coli and Enterobacteriaceae have been used as indicator organisms to monitor the potential fecal contamination of water. Previous studies have shown that both the E. coli and the Enterobacteriaceae counts might be significantly different when water is sampled at different times of the day. It has also been proposed that sediments might contain higher levels of indicator microorganisms than the surface water, and may be one of the reasons causing fluctuations reported in bacterial enumeration.

Purpose: To better understand the fluctuations seen from bacterial enumeration and the role sediments may play in water quality monitoring, this study chose two lakes in the state of Alabama as models and examined their water quality.

Methods: At each lake, two sampling spots were chosen. Fifty ml of surface water and 25 g of sediment from each sample site were collected and plated using 3M^TM Coliform/E. coli Petrifilm and 3M^TM Enterobacteriaceae Petrifilm. The concentrations of the indicator microorganisms were enumerated following the manufacture’s manual. In addition, one ml of surface water was collected using a disposable Transfer Pipet and plated using E. coli Coliscan Easygel® for parallel comparison with the 3M method.

Results: Results showed that both the sampling time (morning vs. afternoon) and sample types (sediment vs. surface water) impacted the enumeration results (P < 0.05). Because the Enterobacteriaceae group covers bacteria such as Salmonella and Shigella, the numbers of Enterobacteriaceae in water and sediment were always higher than the total E. coli/Coliform (P< 0.05).  

Significance: The results of this study indicate that a more accurate sampling method and sampling schedule are still needed in order to better monitor water quality, especially the water used for irrigation purposes and direct body contact.