Twenty years of research into Chlamydia-like organisms: a revolution in our understanding of the biology and pathogenicity of members of the phylum Chlamydiae

• Published in: Pathogens and disease 2015-02, Vol.73 (1), p.1-15
• Main Authors: Taylor-Brown, Alyce, Vaughan, Lloyd, Greub, Gilbert, Timms, Peter, Polkinghorne, Adam
• Format: Article
• Language: English
• Subjects: Animal diseases; Animals; Biology; Biomedical Research - history; Biomedical Research - trends; Cell culture; Cell survival; Chlamydia; Chlamydiae; Chlamydiales - classification; Chlamydiales - pathogenicity; Chlamydiales - physiology; Diagnostic systems; Environmental Microbiology; Genomes; Gram-Negative Bacterial Infections - microbiology; Gram-Negative Bacterial Infections - veterinary; History, 20th Century; History, 21st Century; Humans; Intracellular; Organisms; Pathogenicity; Pathogens; Sexually transmitted diseases; STD
• ISSN: 2049-632X; 2049-632X
• DOI: 10.1093/femspd/ftu009

Chlamydiae are obligate intracellular bacteria that share a unique but remarkably conserved biphasic developmental cycle that relies on a eukaryotic host cell for survival. Although the phylum was originally thought to only contain one family, the Chlamydiaceae, a total of nine families are now recognized. These so-called Chlamydia-like organisms (CLOs) are also referred to as ‘environmental chlamydiae’, as many were initially isolated from environmental sources. However, these organisms are also emerging pathogens, as many, such as Parachlamydia sp., Simkania sp. and Waddlia sp., have been associated with human disease, and others, such as Piscichlamydia sp. and Parilichlamydia sp., have been documented in association with diseases in animals. Their strict intracellular nature and the requirement for cell culture have been a confounding factor in characterizing the biology and pathogenicity of CLOs. Nevertheless, the genomes of seven CLO species have now been sequenced, providing new information on their potential ability to adapt to a wide range of hosts. As new isolation and diagnostic methods advance, we are able to further explore the richness of this phylum with further research likely to help define the true pathogenic potential of the CLOs while also providing insight into the origins of the ‘traditional’ chlamydiae. This manuscript reflects on our progress in understanding the biology, evolution, adaptation and pathogenesis of Chlamydia-like organisms, 20 years following their initial identification and description.