Gardnerella vaginalis
Gardnerella is a genus of Gram-variable-staining facultative anaerobic bacteria of which Gardnerella vaginalis is the only species. The organisms are small (1.0–1.5 μm in diameter) non-spore-forming, nonmotile coccobacilli. Once classified as "Haemophilus vaginalis" and afterwards as "Corynebacterium vaginalis", "G. vaginalis" grows as small, circular, convex, gray colonies on chocolate agar; it also grows on agar. A selective medium for "G. vaginalis" is colistin-oxolinic acid blood agar. Clinical significance. "G. vaginalis" is a facultatively anaerobic Gram-variable rod that is involved, together with many other bacteria, mostly anaerobic, in bacterial vaginosis in some women  as a result of a disruption in the normal vaginal microflora. The resident facultative anaerobic "Lactobacillus" population in the vagina is responsible for the acidic environment. Once the anaerobes have supplanted the normal vaginal bacteria, prescription antibiotics with anaerobic coverage may have to be given to re-establish the equilibrium of the ecosystem. "G. vaginalis " is not considered the cause of the bacterial vaginosis, but a signal organism of the altered microbial ecology associated with overgrowth of many bacterial species. While typically isolated in genital cultures, it may also be detected in other samples from blood, urine, and the pharynx . Although "G. vaginalis" is a major species present in bacterial vaginosis, it can also be isolated from women without any signs or symptoms of infection. It has a Gram-positive cell wall, but, because the cell wall is so thin, it can appear either Gram-positive or Gram-negative under the microscope. It is associated microscopically with clue cells, which are epithelial cells covered in bacteria. "G. vaginalis" produces a pore-forming toxin, vaginolysin, which affects only human cells. Protease and sialidase enzyme activities frequently accompany "G. vaginalis". Treatment. Methods of antibiotic treatment include metronidazole and clindamycin, in both oral  and vaginal gel/cream forms. The effectiveness of treating bacterial vaginosis with antibiotics is well documented. Symptoms. "G. vaginalis" is associated with bacterial vaginosis, which may be asymptomatic, or may have symptoms including vaginal discharge, vaginal irritation, and a "fish-like" odor. In the amine whiff test, 10% KOH is added to the discharge; a positive result is indicated if a fishy smell is produced. This and other tests can be used to distinguish between vaginal symptoms related to "G. vaginalis" and those caused by other organisms, such as "Trichomonas" and "Candida albicans", which are similar and may require different  treatment. "Trichomonas vaginalis" and "G. vaginalis" have similar clinical presentations and can cause a frothy gray or yellow-green vaginal discharge, pruritus, and produce a positive "whiff-test". The two can be distinguished using a wet-mount slide, where a swab of the vaginal epithelium is diluted and then placed onto a slide for observation under a microscope. "Gardnerella" reveals a classic "clue cell" under the microscope, showing bacteria adhering to the surface of squamous epithelial cells. Eponym. It is named after Hermann L. Gardner (1912–1982), an American bacteriologist who discovered it in 1955.