Gardnerella is a genus of gram-variable bacteria of which Gardnerella vaginalis is the only species. Gardnerella vaginalis can cause bacterial vaginosis in some women.

Once classified as a species of Haemophilus, G. vaginalis grows as small, circular, convex, gray colonies on Chocolate agar; it will also grow on HBT agar. A selective medium for G. vaginalis is colistin-oxolinic acid blood agar.

While typically isolated in genital cultures, it may also be detected from other sources, such as blood, urine and pharynx. Although a chief cause of bacterial vaginosis, it may be isolated from women without any signs or symptoms of infection.

Under the microscope it appears as a gram-negative rod, although it has been reported to have a gram-postive cell wall. It is associated microscopically with clue cells, which are epithelial cells covered in bacteria.