Lactobacillus rhamnosus is a bacterium that originally was considered to be a subspecies of Lactobacillus casei, but genetic research found it to be a species of its own. It is a short Gram-positive heterofermentative facultative anaerobic non-spore-forming rod that often appears in chains. Some strains of Lactobacillus rhamnosus bacteria are being used as probiotics, and are particularly useful in treating female-related infections, most particularly very difficult to treat cases of bacterial vaginosis (or "BV"). The Lactobacillus rhamnosus and L. reuteri species are most commonly found in the healthy female genitourinary tract and are most helpful to supplement in order to regain control over dysbiotic bacterial overgrowth during an active infection. L. rhamnosus sometimes is used in yogurt and dairy products such as fermented and unpasteurized milk and semi-hard cheese. While frequently considered a beneficial organism, Lactobacillus rhamnosus may not be as beneficial to certain subsets of the population; in rare circumstances, especially those primarily involving weakened immune system or infants, it may cause endocarditis.