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C. trachomatis is a strict human pathogen.
C. trachomatis are Gram-negative bacteria. However, they canbe stained better by Giemsa, Castaneda, Machiavello, or Gimenez stains. C. trachomatis like other chlamydiae occurs in two morphologically distinct forms: elementary body and reticulate body.
EB is an extracellular infectious particle. It is small and spher-ical and measures 800–1200 nm in diameter. These inclusion bodies in the infected cells, such as conjunctiva, urethra, and corneal smears can be demonstrated after staining with Giemsa, Castaneda, or Machiavello methods. These inclusion bodies are large-sized particles, which can be easily demonstrated under light microscope. These bodies consist of glycogen matrix, hence are demonstrated on staining with Lugol’s iodine.
Reticulate body is metabolically active and replicating form of Chlamydia.
C. trachomatis grows better in various tissue cultures, usingnonreplicating stationary-phase cells. The bacteria can grow in a few cell lines, such as HeLa-229, McCoy, BHK-21, and buffalo green monkey kidney cells. McCoy and HeLa cells are frequently used for the isolation of the bacteria.
C. trachomatis can be grown by inoculation into embryo-nated eggs and also by experimented infection in animals, such as mice. Chlamydia spp. grow in yolk sac of 6–8 days old chick embryo. The growth of chlamydia is demonstrated by the pres-ence of elementary and inclusion bodies as well as group-spe-cific complement-fixing antigen in the yolk sac.
C. trachomatis strains differ in their infectivity (L1, L2, and L3)and cause infection in mice when injected intracellularly.
Susceptibility to physical and chemical agents: Chlamydiaeare heat-labile bacteria and are readily killed within minutes by heating at 56°C. They are susceptible to ethanol, ether, phenol, formalin, iodine, potassium permanganate, sodium hypochlorite, silver nitrite, and chlorite. They remain fully viable for several days at 4°C. Moreover, they can be preserved at270°C or in liquid nitrogen for a long period.
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