Bacterial vaginosis is characterized by a thin malodorous vaginal discharge due to an alteration of bacterial flora caused by a shift in the acidity (pH) of the vagina. It's referred to as a 'vaginosis' rather than an 'vaginitis' because 'itis' implies an inflamation which would be accompanied by a proliferation of white blood cells (wbc's). Here, in a bacteria vaginosis, the bacteria flourish without a significant increase in wbc's.
A several markers provide clues in the diagnosis of bacterial vaginosis.
- Potassium hydroxide - a drop added to sample of the discharge produces a fishy odour due to amines released.
- pH measurement - loss of normal acidity (generally considered >4.5) may suggest a vaginosis diagnosis, however it is not very definitive therefore not usually done in the lab.
- Observation and bacterial enumeration of genera present in a vaginal gram stain. Vaginosis is characterized by a decrease by the lactic acid producing lactobacilli (hence the name) and an increase in the specific organisms, Gardnerella vaginalis, Mobiluncus species, and anaerobic organisms such as Bacterioides & Prevotella species. The relative proportion and or presence of these organisms can suggest bacterial vaginosis.
- Clue Cells - the presence of epithelial cells stippled with gram variable bacilli is suggestive of bacterial vaginosis. In Scanning the gram stain, the presence of these epithelial cells coated with gram variable bacilli appear purplish in comparison to the regular pinkish-red epithelial cells present. Why these bacteria tend to adhere is not fully understood.
- Probably the most noticeable bacterial form present in bacterial vaginosis is referred to as 'gram variable' bacilli. These are the Gardnerella vaginalis bacteria whose individual cells can stain both purple and red with the gram stain. That is, some entire cells may be either gram positive (purple-blue) or gram negative (pinkish-red) or both. They are relatively small or short cells. The irregular gram staining properties historically have contributed to placing the organisms in different genera. Previously called both Corynebacterium vaginale (a gram positive genera), and Haemophius vaginalis, (a gram negative genera), before being given it's own genera of Gardnerella. It is a somewhat fastidious organism.
- Mobiluncus species - various species of the genus may be present in bacterial vaginosis and are observed, if present, as gram negative curved bacilli.
- Anaerobic bacteria such as Bacteroides and Prevotella also are disproportionate and can be seen as smaller straight gram negative bacilli
- Lactobacillus species are regular gram positive bacilli (purple-blue rods) which can vary in shape depending on the species and environment. The lactic acid they produce within the healthy vagina keep it slightly acidic which restricts the growth of other species of bacteria.
By scoring the various bacterial forms and noting the presence of Clue Cells, one can standardize the criteria for determining if the patient does indeed have bacterial vaginosis.
While bacterial vaginosis is a genital, or perhaps a sexual disease, it is not considered a sexually transmitted disease. Sexual contact is not responsible for it's presence nor is it spread through sexual contact. It arises from changes within host allowing for the disproportionate proliferation of native bacterial species.
Now for some photos of what is described above;
Gram stain showing a couple of epithelial cells and numerous gram positive lactobacilli (purple rods). Note too that there are few if any white blood cells.
(100X, Gram Stain, Nikon)
Normal Vaginal Flora
All epithelial cells appear similar with no 'Clue Cells' which would appear bluish due to all the
Gardnerella vaginalis organisms adhering to the cells.
(100X, Gram Stain, Nikon)
Gram of bacterial vaginosis
Gram stain (1000X enlarged) showing epithelial cell coated with gram variable bacilli (Clue Cell).
Note gram variable bacilli (Gardnerella vaginalis) , gram negative curved bacilli (Mobiluncus sp.) & regular gram negative bacilli. Straight gram positive lactobacilli as seen in the previous photo are absent.
(1000X, Gram Stain, Nikon)
08/10/11: As an afterthought I added this photo which may better illustrate what is referred to as a 'Clue Cell' in vaginal swab gram stains. Here two epithelial cells are seen however the one on the left is 'coated' with gram variable bacilli (Gardnerella vaginalis) making the cell appear purplish. On lower power scanning, these are usually seen with some frequency in a patient experiencing bacterial vaginosis.
(1000X, Gram Stain, Nikon)
A couple enlarged (1000X) gram stains of gram variable bacilli.
Small, short cells are gram variable -gram negative (pink), gram positive (blue) or both at once.
Gram Stain (1000X) of Mobiluncus species (curtisii)
(Click on photo to enlarge for better viewing)
Mobiluncus species contribute to Bacterial vaginosis. They appear as gram negative (pink) curved bacilli - (look like pink parentheses)
Present are also two large pink epithelial cells
For direct comparison
(Both 1000X, Gram Stain)
Just for comparison: Vaginal Gram Stain of Yeast Infection (1000X)
Note: epithelial cells with yeast cells (purple) and yeast pseudohyphae (long purple thread-like structure).
My Related Papers;
Relative Susceptibilities of Gardnerella vaginalis (Haemophilus vaginalis), Neisseria gonorrhoeae and Bacteroides fragilis to Metronidazole and Its Two Major Metabolites.
Metronidazole In Treatment against Haemohilus vaginalis (Corynebacterium vaginale)