Bacterial vaginosis. Light micrograph of a cervical smear from a patient with bacterial vaginosis. An epithelial cell (pink, centre) is covered in Gardnerella vaginalis bacteria (rods), one of the species of bacteria that cause vaginosis. Bacterial vaginosis causes an abnormal vaginal discharge with an unpleasant fishy smell. It is caused by an imbalance of the normal vaginal flora. Treatment is with antibiotics.