Lipopolysaccharides (LPS), also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals. Chlamydia trachomatis, an obligate intracellular human pathogen, is one of three bacterial species in the genus Chlamydia. C. trachomatis is a Gram-negative bacteria, therefore its cell wall components retain the counter-stain safranin and appear pink under a light microscope. The inclusion bodies of Chlamydia trachomatis were first described in 1907, the Chlamydia trachomatis agent was first cultured in the yolk sacs of eggs by Feifan Tang et al in 1957. Chlamydial infection. Advances in the diagnostic isolation of Chlamydia, including TRIC agent, from the eye, genital tract, and rectum. trachomatis includes three human biovars: trachoma (serovars A, B, Ba or C), urethritis (serovars D-K), and lymphogranuloma venereum (LGV, serovars L1, 2 and 3). Many, but not all, C. trachomatis strains have an extrachromosomal plasmid.