Animated coloured scanning electron micrograph (SEM) of Streptococcus thermophilus, Gram-positive, coccoid prokaryote (bacterium). Streptococcus thermophilus (also known as: Streptococcus salivarius subsp. thermophilus) is a facultative anaerobe that belongs to a group of lactic acid bacteria that convert lactose to lactic acid and acetaldehyde. Streptococcus thermophilus and Lactobacillus bulgaricus are used as a starter culture for the manufacture of several important fermented dairy foods, including yogurt and Mozzarella cheese. S. thermophilus is found in milk and milk products. It also has an important role as a probiotic, alleviating symptoms of lactose intolerance and other gastrointestinal disorders.