Fluorescence micrographs of epithelial cells recovered from the vaginas of human volunteers. (a) A single epithelial cell with highly refractile blood cells (the volunteer was menstruating) and colonized by rod-shaped and coccoid bacteria. (b) A similar cell reacted with the fluorescent eubacterial domain (EU 338) probe, whose base sequence reacts with the 16S RNA of all eubacteria, including both lactobacilli and staphylococci. (c) The same cell as in a reacted with a fluorescent probe that reacts only with the 16S RNA of S. aureus. This organism was found in the vaginal flora of all volunteers tested, and this result was confirmed by PCR. Figures reproduced with permission from the Journal of Infectious Diseases (36).