VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

MORPHOLOGY

• Chlamydiae occur in two forms, elementary bodies and reticulate bodies.

Developmental cycle of Chlamydiae

• They have a unique developmental cycle with alternating, morphologically distinct, infectious and reproductive forms.
• The elementary bodies (EB) are small, spherical 200-300nm in d.m., infectious and represents the extracellular form of the organism.
• The elementary bodies enters a cell by endocytosis and differentiate into the large (500 –1000nm size), non infectious, but metabolically active reticulate body (RB) inside an expanding vacuole.
• The RB multiplies by binary fission producing further RB’s.
• At about 20hrs following infection, some of the RB’s start to condense and mature within the inclusion to form EB’s.
• In general, release of infectious EB’s begins at about 40hrs post infection due to lysis of the cell.
• Chlamydiae are Gram negative; the EBs can be demonstrated by the use of either chemical stains or FAT and IPT.
• In modified ZN stain the EBs tend to occur in clumps and stain red against a blue background.
• When the modified ZN stained smears examined under darkfield microscopy, the EBs appears as bright green, coccal structures.
• In methylene blue stain under dark field illumination the EBs show autofluorescence, they are revealed as refractile, yellow green bodies surrounded by a halo.
• In machiavello stain, the EBs stain red against a blue background. In castanedas stain, the EBs are stained blue with a reddish background.
• Giemsa stain: Particularly useful in smears from conjuctival swab of feline pneumonitis cases.
• Infected conjuctival epithelial cells contain basophilic intracytoplasmic aggregates of C.psittaci.