To test water safety at swimming beaches, workers take water samples,
filter them to collect the bacterial cells, and place them on a culture
medium that promotes the growth of only enterococcus bacteria—an
indicator of contamination. Single cells can grow explosivley into
colonies (blue because of a pH-indicator dye in the medium).
Massachusetts bathing beach regulations set the limit for enterococcus
cells in beach waters at 104 "colony forming units" in 100 millimeters.
(Courtesy of Bethany Sadlowski, Barnstable County Department of Health and Environment)[back]
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