The Chlamydiaceae are a family of bacteria that belongs to the phylum Chlamydiae, order Chlamydiales. All Chlamydiaceae species are Gram-negative and express the family-specific lipopolysaccharide epitope αKdo-(2→8)-αKdo-(2→4)-αKdo (previously called the genus-specific epitope). Chlamydiaceae ribosomal RNA genes all have at least 90% DNA sequence identity. Chlamydiaceae species have varying inclusion morphology, varying extrachromosomal plasmid content, and varying sulfadiazine resistance.