Bacillales
Lactobacillales The term bacilli (singular bacillus) is used to refer to any rod-shaped bacteria. As a formal taxon, the Bacilli (capitalized) are a class of Firmicutes, including Bacillus and various other Gram-positive bacteria, such as Staphylococcus and Listeria.

The Bacilli are distinguished from the Clostridia by aerobic respiration. Their relationships are still somewhat uncertain, and they appear to be paraphyletic, giving rise to the Mollicutes and possibly others. They may form two separate groups, forms like Bacillus that produce endospores and forms that do not, including the Lactobacillales.