Enhanced detection of bacteria in natural environments by fluorochrome staining of DNA1

The DNA‐staining fluorochromes 4′6‐diamidino‐2‐phenylindole (DAPI) and mithramycin, when used in conjunction with epi‐illumination fluorescence microscopy, readily reveal the presence of bacteria, thus simplifying the detection of bacterial contaminants in allegedly axenic laboratory cultures of eucaryote cells. Both gram‐negative and gram‐positive cells are stained, and aqueous solutions of the dyes penetrate living as well as fixed cells. The use of an epi‐illumination system for fluorescence microscopy makes it possible to scan the microflora epiphytic on material collected from freshwater or marine environments, even when the thickness of the material renders both phase and Nomarski optics inadequate.