Enumeration of Bacteria in Sea Water

The choice of methods to be used for the enumeration of bacteria in sea water must depend on the objectives of the investigators. Comparisons of data based on different methods may be invalid. An operational definition is given for a colony-generating unit (CGU) which, under some conditions, may be a single viable bacterium. Such units can conveniently be enumerated by a modification of the “minimum probable number” method currently employed in aquatic bacteriology. Counts of “viable bacteria” (CGU) in surface sea water samples from the region of the North Pacific Gyre (28° N, 155°W) were estimated to range from 10,000 to 200,000 per litre.