Kingdom-Monera

Division-Firmicutes

Class-Bacilli

Order-Lactobacillales

Family-Lactobacillaceae

Genus-Lactobacillus

Species-L. Acidophilus

Lactobacillus acidophilus is part of the kingdom Monera, which is the only kingdom of prokaryotic organisms.  It is also in the division Firmicutes, which has species that produce endospores, and all are found in many different environments.  All bacteria in the Firmicutes division are Gram positive, which means that they retain a purple iodine-dye used in certain staining techniques.  L. acidophilus is in the class Bacilli, which contains many beneficial bacteria.  L. acidophilus belongs to the order Lactobacillales, which includes species found in soil, water, plants, and animals.  Species in the order of Lactobacillales are also widely used in fermentation.   The family Lactobacillaceae, in which L. acidophilus belongs, is a family of lactic-acid bacteria, who all produce lactase, and enzyme that breaks down complicated milk sugars into simpler sugars.  The L. acidophilus belongs to the genus Lactobacillus, in which many species are prominent in decaying plant material, and all are found in the human gastrointestinal tract.