Mab ACI recognizes a genus-specific epitope of the Chlamydia lipopolysaccharide antigen and identifies all serovars (A-C, D-K, L1-L3) of C. trachomatis as well as Chlamydophila psittaci and Chlamydophila pneumoniae with a strong fluorescence of the intracellular inclusions, the pinhead-sized extracellular elementary bodies and the free cell-associated Chlamydia lipopolysaccharide antigens (amorphous foci). A positive cross-reactivity was al-so reported for Chlamydophila pecorum.