Lactobacillus bacteria. Coloured scanning electron micrograph (SEM) of the lactic acid-producing bacteria Lactobacillus sp. (blue). Also seen are unidentified cocci (oval) bacteria. Lactobacillus are rod-shaped Gram-positive lactic acid producing bacteria. They sour milk and are used extensively in the food industry, such as in bread, cheese and yoghurt production. Lactobacillus occur naturally and harmlessly in humans and animals. They are part of the vaginal and intestinal flora and are non-pathogenic. Magnification: x9000 at 6x7cm size.