Treponema pallidum- Morphology, cultural characters, Biochemical Structure, Epidemiology

Class- Spirochaetes (Speira =coil; chaite=hair)

Order- Spirochaetales

Family- Spirochaetaceae

Genus- Treponema

Human pathogens are found in the genera Treponema, Borrelia & Leptospira

Treponemes

Family- Spirochaetaceae         Genus- Treponema

-short, slender spirochetes; exist as pathogens  or commensals 

-pathogens which cause diseases in man,

• Venereal syphilis - T. pallidum

• Endemic syphilis - Treponema endemicum
• Yaws- Treponema pertenue
• Pinta- Treponema carateum

Treponema pallidum (Trepo = turn Nema=thread; pallidum- pale staining property)

1905 -Fritz Schaudinn and Paul E. Hoffmann discovered Treponema pallidum in chancres (ulcers) and in inquinal (groin region) lymph nodes of the patients

Morphology of Treponema pallidum

• Gram negative, thin, delicate, helically coiled, spirochete with tapering ends
• corkscrew-shaped
• about 10 spirals, sharp and angular, at regular intervals of about 1 micrometer
• microaerophilic and actively motile
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Microscopy

• Live Treponemes cannot be visualized under conventional light microscope in wet films
• Negative staining with Indian Ink.
• Morphology and motility can be visualized by using dark-field or phase contrast microscopy
• Pale staining properties- Stain light rose red with prolonged Giemsa staining
• Silver impregnation methods used to better visualise the organism- Fontana’s method for staining films & Levaditi’s method for tissue sections

Ultra Structure

• Trilaminar cytoplasmic membrane enclosed by a cell wall containing peptidoglycans which gives the cell rigidity and shape-Protoplasmic cylinder running through entire length of organism
• From each end of cell, 3-4 endoflagella - Endoflagella do not protrude outside, but remain within Outer membrane layer.

• Has nucleoid, ribosomal structures and other cytoplasmic materials
• Outer membrane is lipid rich and contains some trans membrane proteins- Differs from most gram negative bacteria in that it lacks lipo-polysaccharide (LPS) membrane proteins
• Bacterium is covered by a muco-polysaccharide “slime layer” or by host derived proteins, thus blocking binding of specific antibodies to surface antigens.

 Cultural Characteristics of Treponema pallidum

• This organism has not been successfully cultured in vitro
• Do not grow in artificial culture media- limited replication has been obtained by co-cultivation with tissue culture cells.
• Viable organisms can be maintained for 10 to 12 days in complex media under anaerobic conditions
• Virulent strains have been maintained for many decades by serial testicular passage in rabbits (Nichol’s strain)- used for diagnostic and research purpose
• Non-pathogenic treponemes eg., Reiter treponeme (T. phagedenis) grows well in thioglycollate medium containing serum- used for group specific Treponemal tests

Biochemical Structure 

•  Treponema is composed of approximately 70 % proteins, 20 % lipids, and 5 % carbohydrates
• Lipid content is relatively high. 
• Lipid composition of T pallidum is complex, consisting of several phospholipids, including cardiolipin, and a poorly characterized glycolipid

Epidemiology

• Worldwide in distribution-highly virulent with cutaneous manifestations
• No extrahuman reservoir- antibiotics like Penicillin were hoped to control the disease, but did not
• Changing customs, values and habits in society has increased its incidence
• AIDS and concurrent infection with syphilis is common-lead to earlier evolution of neurosyphilis