ABSTRACT
With the advent of electron microscopy in the 1960s, Chlamydiae were classified as bacteria, essentially because they possess DNA, RNA, ribosomes, and have a cell wall similar to that of Gram-negative bacteria. As phylogenetically isolated, intracellular microbes, Chlamydiales are believed to have evolved differently than other well-characterized facultative and obligate intracellular eubacteria. The genus Chlamydia is marked by the presence of intracellular glycogen, unfortunately those formally of the genus Chlamydophila are marked by neither the presence nor the absence of glycogen since some species show transient levels of glycogen during their life cycle. The order Chlamydiales contains the Chlamydiaceae and the Candidatus Clavichlamydiaceae families. Although clinicians consider Chlamydiae culture methods to be the gold standard for identification of chlamydial infection, it has low specificity and it is laboratory expertise-dependent. Zoonotic chlamydial infection is rare and it may be underestimated secondary to faulty isolation and detection practices.
