Use of the direct epifluorescent filter technique for the enumeration of bacterial spores.

Heat treatment at 80 degrees C for 10 min effectively destroyed all vegetative cells (except for Gram-positive cocci) and made easier the counting of bacterial spores, which stained orange, green or rarely transparent/black with a dull green halo, in the direct epifluorescent filter technique. The numbers of both orange- or green-staining spores were lower than the plate count. A variety of physiological conditions were used to investigate the relationship of the different staining patterns with germination status. It was concluded that orange-staining spores had germinated and their number agreed with the plate count after incubation in yeast glucose broth at 30 degrees C for 4 h. This observation was unreliable, however, but it was found that a total spore count in the DEFT gave a good agreement with the plate count.