Chlamydia and Chlamydiales: more than meets the eye

This review summarizes the dramatic changes that have occurred in the taxonomy of bacteria known as Chlamydia. Best known for the diseases they cause in humans, these intracellular bacteria also comprise many species that are responsible for a wide variety of clinically and economically important diseases in livestock and companion animals. The old taxonomy grouped most of these species into C. psittaci because systematic methods for routinely distinguishing them were not available. DNA-based testing methods are now available that distinguish different chlamydial families, genera, and species. This summary reviews these tests and a number of oligonucleotide primers that distinguish these groups using PCR and PCR-RFLP. DNA-based methods are also being used to discover new families of chlamydia-like bacteria, at least one of which is responsible for abortion in cattle (Waddlia chondrophila). This review summarizes the pathogenic roles of the Chlamydiaceae, new families, and individual species within the order Chlamydiales. These discoveries create opportunities for veterinarians to carry out epidemiological studies of chlamydiae that previously were not possible.