Chlamydia trachomatis

The obligate intracellular bacterium Chlamydia trachomatis is arguably the most common sexually transmitted bacterial pathogen worldwide and a major cause of blindness in underdeveloped countries. Urogenital chlamydial infection is mostly asymptomatic or exhibits very mild symptoms. However, if left untreated, it can result in devastating complications, with tubal factor infertility and pelvic inflammatory diseases being the most common outcomes, and ectopic pregnancy being the most dangerous consequence. Like other chlamydiae, C. trachomatis has a unique developmental cycle, which consists of two distinct cellular forms, and is accompanied by a temporal expression pattern of genes and small non-coding RNAs. C. trachomatis strains display strikingly different tissue tropisms, which correlate with a small number of genes differentially existing in their genomes. A conserved plasmid has been identified as a critical virulence factor. A long-awaited transformation system developed on the basis of the plasmid is anticipated to greatly facilitate the understanding of chlamydial biology in coming years.