Genus Chlamydia.

Chlamydia trachomatis

The first chlamydial agent to be discovered. C. trachomatis is comprised of two human biovars: the trachoma and lymphogranuloma venereum (LGV). The mouse and swine strains that were previously grouped with this species now belong to separate species (C. muridarum and C. suis, respectively). Serovars in both C. trachomatis biovars cause trachoma, sexually transmitted disease, some forms of arthritis, and neonatal inclusion conjunctivitis and pneumonia [see: infections index]. The trachoma biovar currently has 14 serovars and infection is limited primarily to epithelial cells of mucous membranes. It has also been detected in posterior bilaminar tissue removed from patients with disease of the temporomandibular joint. The LGV biovar consists of four serovars, L1, L2, L2a and L3, which can invade lymphatic tissue. C. trachomatis strains have a high degree of sequence conservation in the genes that have been characterized (e.g. 16S-rRNA genes differ by < 0.65%). The complete gene sequences of two strains have been sequenced: D/UW-3/CX (1 042 519 bp) and L2/434/BU (1 038 680 bp). The gene for MOMP, ompA (omp1), is widely used to distinguish C. trachomatis strains by both DNA amplification techniques and serotyping. Many, but not all, C. trachomatis strains have an extrachromosomal plasmid. Chlamydia species are readily identified and distinguished from other species by comparison of ribosomal gene sequences that have been designated as ‘signature sequences’ (Everett et al., 1999 ) or by inspection of the 16S–23S-rRNA intergenic spacer (Everett and Andersen, 1997). C. trachomatis strains are generally sensitive to sulfadiazine and tetracyclines. Most strains of C. trachomatis are recognized by monoclonal antibodies [mAbs] to epitopes in the VS4 region of  MOMP. However, these mAbs may also crossreact with C. suis or C. muridarum (below).

Chlamydia suis

C. suis has only been isolated from swine, where it causes conjunctivitis, enteritis, pneumonia, and a high incidence of apparently asymptomatic infection. Some strains are resistant to sulfadiazine and/or tetracycline. Several strains of C. suis are known to have an extrachromosomal plasmid, pCS. DNA sequence analysis of ompA indicates that C. suis strains are somewhat more diverse than are other chlamydial species. The deduced ompA gene products of various C. suis strains contain VS4 epitopes nearly identical to epitopes recognized by C. trachomatis VS4 mAbs and B-serogroup mAbs. Because these mAbs are routinely used to serotype human C. trachomatis isolates, this crossreaction may lead to errors in species identification.

Chlamydia muridarum sp. nov., including hamster and mouse isolates previously belonging to Chlamydia trachomatis

Two strains of C. muridarum, MoPn and SFPD have been isolated from mice and hamsters. MoPn infection may be asymptomatic or produce pneumonia in mice. SFPD is an enteric isolate and was obtained concurrently with a causative agent of proliferative ileitis. MoPn is sensitive to sulfadiazine and its glycogen production is difficult to detect. MoPn has an extrachromosomal plasmid, pMoPn. The C. trachomatis MOMP VS4 core epitope (T)LNPT(IA) is present in both strains, and B-serogroup mAbs specific for the VS4 epitope IAGAG should also recognize SFPD.

[KDE & MEW] May 2002

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