Vaginal bacteria. Coloured scanning electron micrograph (SEM) of bacteria cultured from a human vagina. 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 but multiply abnormally quickly, causing thrush or vaginosis, for example. Magnification: x1000 when printed at 10 centimetres wide.