Class Bacteroides
   Bacteroidales
Class Flavobacteria
   Flavobacteriales
Class Sphingobacteria
   Sphingobacteriales
The phylum Bacteroidetes is composed of three large groups of bacteria. By far, more is written about and known about the Bacteroides class, than the other two, the Flavobacteria and the Sphingobacteria classes. They are related by the similarity in the composition of the small 16S subunit of their ribosomes. Members of the bacteroides class are human commensals and sometimes pathogens. Rarely are members of the other two classes pathogenic to humans.