Biology and Infection of Treponema

Treponema

The genus Treponema includes T pallidum subspecies pallidum , which causes syphilis; T pallidum subspecies pretense , which causes yaws; T pallidum subspecies endemicum , which reasons endemic syphilis (additionally referred to as bejel); and Treponema carateum, which reasons pinta.

Treponema pallidum

Typical Organisms

T pallidum is slim spirals measuring about zero.2 m in width and 5–15 m in duration. The spiral coils are regularly spaced at a distance of 1 m from one another. Th e organisms are actively motile, rotating progressively round their endo flagella even after attaching to cells by their tapered ends. The lengthy axis of the spiral is ordinarily immediately, however, may additionally once in a while bend so that the organism paperwork an entire circle for moments at a time, returning then to its normal instantly position. Th e spirals are so thin that they are now not comfortably seen except immunofl uorescent stain or darkish-fi eld illumination is used. They do now not stain nicely with aniline dyes, but they can be visible in tissues while stained by a silver impregnation approach.

Culture

Pathogenic T pallidum has never been cultured continuously on artificial media, in fertile eggs, or in tissue culture. Nonpathogenic treponemes (eg, Reiter stress) may be cultured anaerobically in vitro. Th ey is saprophytes antigenically associated with T pallidum.

Cultural characteristics

T pallidum is a microaerophilic organism; it survives first-class in 3–5% oxygen. Th e saprophytic Reiter strain grows on a defined medium of eleven amino acids, nutrients, salts, minerals, and serum albumin. In right postponing fluids and within the presence of reducing materials, T pallidum may continue to be motile for three–6 days at 25ï‚°C. In complete blood or plasma stored at 4ï‚°C, organisms remain possible for as a minimum 24 hours, which is of ability significance in blood transfusions.

Reactions to physical and Chemical Components

Drying kills the spirochete swiftly, as does elevation of the temperature to 42ï‚°C. Treponemes are rapidly immobilized and killed with the aid of trivalent arsenical, mercury, and bismuth (contained in pills of the historical hobby in the treatment of syphilis). Penicillin is treponemicidal in minute concentrations, however, the price of killing is slow, possibly because of the metabolic inactivity and slow multiplication fee of T pallidum (expected department time is 30 hours). Resistance to penicillin has not been verified in syphilis.

Genome

The T pallidum genome is a circular chromosome of about 1,138,000 base pairs, which is small for bacteria. Most pathogenic microorganisms have transposable elements, but T pallidum does now not, which shows that the genome is distinctly conserved and can give an explanation for its endured susceptibility to penicillin. There are few genes concerned in electricity manufacturing and synthesis of nutrients, indicating that T pallidum obtains these from the host.

Antigenic shape

The truth that T pallidum can not be cultured in vitro has markedly restrained the characterization of its antigens. The outer membrane surrounds the periplasmic space and the peptidoglycan–cytoplasmic membrane complex. Membrane proteins are present that comprise covalently sure lipids at their amino terminals. The lipids seem to anchor the proteins to the cytoplasmic or outer membranes and keep the proteins inaccessible to antibodies. The endo flagella are in the periplasmic area. T pallidum subspecies pallidum has hyaluronidase that breaks down the hyaluronic acid inside the floor substance of tissue and probably enhances the invasiveness of the organism. The protein profiles of T pallidum (all of the subspecies) are indistinguishable; more than a hundred protein antigens had been referred to. The endo flagella are composed of three core proteins which can be homologous to different bacterial flagellin proteins plus an unrelated sheath protein. Cardiolipin is a critical issue of the treponemal antigens. People with syphilis increase antibodies capable of staining T pallidum by way of oblique immunofluorescence, immobilizing and killing stay motile T pallidum and solving complement in the presence of a suspension of T pallidum or associated spirochetes. The spirochetes additionally purpose the improvement of an awesome antibody-like substance, reagin, which offers wonderful complement fixation (CF) and flocculation check outcomes with aqueous suspensions of cardiolipin extracted from ordinary mammalian tissues. both reagin and the antitreponemal antibody can be used for the serologic diagnosis of syphilis.

Pathogenesis, Pathology, and medical Findings

Acquired Syphilis

Natural infection with T pallidum is constrained to the human host. Human contamination is usually transmitted by way of sexual touch, and the infectious lesion is on the pores and skin or mucous membranes of genitalia. In 10–20% of cases, however, the primary lesion is intrarectal, perianal, or oral. it may be everywhere on the body. T pallidum can probable penetrate intact mucous membranes, or the organisms may additionally enter through a damage within the dermis. Based totally on experiments in rabbits, as few as four to 8 spirochetes can also purpose infection. Spirochetes multiply regionally at the web site of entry, and some unfold to nearby lymph nodes and then attain the bloodstream. Within 2–10 weeks after contamination, a papule develops at the web page of infection and breaks all the way down to form an ulcer with a clean, tough base (“hard chancre”). The inflammation is characterized by means of a predominance of lymphocytes and plasma cells. This “number one lesion” continually heals spontaneously, but 2–10 weeks later, the “secondary” lesions seem. These include a purple maculopapular rash everywhere on the body, along with the fingers and toes, and wet, pale papules (condylomas) in the anogenital location, axillae, and mouth. The patient may have syphilitic meningitis, chorioretinitis, hepatitis, nephritis (immune complex kind), or periostitis. The secondary lesions also subside spontaneously. Each number one and secondary lesions are wealthy in spirochetes and are rather infectious. Contagious lesions may also recur within 3–five years after contamination, however there after the individual isn't always infectious. Syphilitic contamination can also stay subclinical, and the affected person may additionally pass via the primary or secondary stage (or each) without symptoms or symptoms but broaden tertiary lesions. In about 30% of instances, the early syphilitic infection progresses spontaneously to complete treatment with out remedy. In every other 30%, the untreated contamination remains latent (basically glaring through high-quality serologic check results). within the the rest, the ailment progresses to the “tertiary degree” characterised by way of the development of granulomatous lesions (gummas) within the skin, bones, and liver; degenerative changes within the imperative nervous device (meningovascular syphilis, paresis, tabes); or cardiovascular lesions (aortitis, aortic aneurysm, aortic valve insufficiency). In all tertiary lesions, treponemes are very rare, and the exaggerated tissue reaction has to be attributed to the allergy to the organisms. But, treponemes can on occasion be determined in the attention or primary fearful gadget in past due syphilis.

Congenital Syphilis

A pregnant girl with syphilis can transmit T pallidum to the fetus through the placenta beginning in the tenth–15th weeks of gestation. Some of the infected fetuses die, and miscarriages end result; others are stillborn at a time period. Others are born live however increase the signs of congenital syphilis in youth, inclusive of interstitial keratitis, Hutchinson’s teeth, saddle nose, periostitis, and a diffusion of crucial apprehensive machine anomalies. good enough treatment of the mom during pregnancy prevents congenital syphilis. The reagin titer in the blood of the child rises with active contamination but falls with time if antibody become passively transmitted from the mother. In congenital contamination, the child makes immunoglobulin M (IgM) anti-treponemal antibody.

Experimental sickness

Rabbits may be experimentally inflamed inside the pores and skin, testis, and eye with human T pallidum. The animal develops a chancre wealthy in spirochetes, and organisms persist in the lymph nodes, spleen, and bone marrow for the whole life of the animal, although there is no revolutionary sickness.

References:

D greenwood, Slack RCB and J Peutherer.Medical microbiology.2001.

JG College, AG Fraser and BP Marmion.Practical Medical microbiology.Fourteenth Edition. Churchill Livingstone, 1996.

JP Micheal, ECS Chan and NR Krieg.Microbiology.Fifth Edition. Delhi: Mcgraw-hill, 1993.

M Cheesbrugh.Medical laboratory manual for tropical countries.London, 2007.