This phylum of bacteria is divided into four classes.
Class Bacilli, families Bacillaceae, Listeriaceae, Staphylococcaceae, Enterococcaceae, Lactobacillaceae, Streptococcaceae
Class Clostridia, families Clostridiaceae, Eubacteriaceae, Peptococcaceae, Peptostreptococcaceae, Ruminococcaceae
Class Erysipelotrichi, family Erysipelotrichidae (genus Erysipelothrix)
Class Mollicutes, orders Acholeplasmatales and Mycoplasmatales