Lactobacillus rhamnosus is a bacterium that originally was considered to be a subspecies of L. casei, but genetic research found it to be a separate species in the L. casei clade. It is a short Gram-positive homofermentative facultative anaerobic non-spore-forming rod that often appears in chains. Some strains of L. rhamnosus bacteria are being used as probiotics, and are particularly useful in treating infections of the female urogenital tract, most particularly very difficult to treat cases of bacterial vaginosis (or "BV").