Use of hoechst dyes 33258 and 33342 for enumeration of attached and planktonic bacteria.

The DNA-specific fluorochromes Hoechst 33258 and 33342 were used to enumerate aquatic bacteria by epifluorescent direct counts. Cultures of estuarine bacteria gave identical counts when stained with Hoechst 33258 or acridine orange, whereas natural populations of aquatic bacteria gave 92 to 98.5% of the acridine orange counts. The technique had distinct advantages over acridine orange when enumerating bacteria on surfaces which bind acridine orange, such as polystyrene.