Any of various rod-shaped, nonmotile aerobic bacteria of the genus Lactobacillus that ferment lactic acid from sugars and are the causative agents in the souring of milk.

• 乳酸杆菌任一种杆状的乳杆菌属的不游动好氧菌，它能使糖发酵产生乳酸，也是牛奶发酸的导因