Vaginitis. Coloured scanning electron micrograph (SEM) of bacteria on the vaginal wall.. Vaginitis is an inflammation of the vagina. The cause is usually a change in the normal balance of vaginal bacteria or an infection. Light bleeding may be present with red blood cells as well as bacteria seen here. A healthy vaginal flora protects the body against urogenital infections. It is made up of many different types of bacteria, the predominant bacteria being lactobacilli. These beneficial or "good" bacteria play a key role in defending against infection. Lactobacilli provide protection against microbes from the external environment, as well as microbes that reside in the vagina. Magnification: x500 when printed at 10 centimetres wide.