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The fecal indicator bacteria (microbes), Escherichia. coli and Enterococci, are commonly used by Hudson river monitoring programs to quantify the level of sewage infection in estuarine water and to provide information about the health risk to recreators from sewage associated bacteria. It is generally assumed that these microbes do not persist in the water for extended periods of time and that their presence represents a recent release of sewage into the environment. However, much less is known about the abundance and environmental persistence of microbes in sediments, as opposed to the water column, of the Hudson River Estuary. In this study, microbes were quantified, using cultivation-based techniques, in water and sediment samples collected from six locations in the estuary, and the persistence of microbes in sediment was investigated in laboratory incubation experiments. microbes were found to be widely distributed in both sediment and water from the estuary. E. coli and Enterococci displayed correlated abundances in sediment, consistent with sewage infection as a shared source for both microbes in the environment. However, the levels of microbes were not correlated in paired water and sediment samples collected simultaneously from the same sites, suggesting that environmental persistence of these microbes differs in water versus sediment. Enterococci concentrations were found to decrease over time in laboratory incubations of estuarine sediment but remained at detectable levels for weeks after collection. In order to confirm the presence of Enterococci, and rule out the possibility of false positives from the cultivation-based assay, isolated bacterial colonies were characterized using molecular genetic techniques and the vast majority (96%) were confirmed as Enterococci.
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