Bacterial vaginosis is an infection whereby micro-organisms which normally inhabit the vagina grow too quickly and become too concentrated. Micro-organisms that can cause bacterial vaginosis are Gardnerella vaginalis and Mobiluncus species. In normal concentrations, these micro-organisms play a role in maintaining vaginal health, but when they grow excessively, they cause bacterial vaginosis. The most common symptom of the disorder is a smelly grey-white discharge.