Lactobacillus bulgaricus bacteria. They are rod-shaped, gram-positive bacteria. They grow in acid media & produce lactic acid from the fermentation of carbohydrates. Lactic acid produced by the fermentation of milk is responsible for the preservation & flavour of cheese, yoghurt & other fermented milk products. The bacteria are found in fermenting animal & plant products & in the alimentary tract & vagina of humans & other animals, where they serve a protective role against more dangerous bacteria.