Lactobacillus acidophilus. Light micrograph of a vaginal smear showing the rod shaped bacteria Lactobacillus acidophilus (blue). These bacteria form the predominant fauna in the vagina of the sexually mature human female. They ferment lactic acid from the glycogen in the epithelial lining of the vagina. The acidic environment that they produce, and live in, inhibits the growth of many other bacterial forms and as such protects the vaginal passageway from infection. Lactobacillus acidophilus is a non-sporing, Gram positive bacteria commonly found growing in chains. Magnification: x1,600 at 35mm size.