Microbiological analysis of Treponema pallidum

What Is Treponema Pallidum: Causes, Symptoms and Complications,Treatment, Prevention

The term ” Treponema” indicates a genus of bacteria to which belong two different pathogenic species, Treponema pallidum and Treponema carateum , microorganisms involved respectively in the onset of syphilis and pinta. Although most of the species belonging to the genus Treponema establish a form of commensalism with the host (resulting as non-pathogenic), Treponema pallidum is distinguished by its characteristic virulence.
Let’s see in more detail the distinctive characters of Treponema pallidum .

Microbiological Analysis Of Treponema Pallidum

An exponent of the phylum Spirochaetes and of the Spirochaetaceae family, Treponema pallidum is a gram-negative bacterium , vector of diseases called trepomatosis, among which light or syphilis stands out. Observed by dark-field or fluorescence microscopy, the bacterium appears as a thin, helical and spiral-shaped microorganism . It has a diameter of 0.1-0.5 microns and a variable length from 5 to 20 microns.

Treponema pallidum is a bacterium sensitive to heat and dry temperatures. In reference to the very poor ability to survive in an oxygen-rich environment, it is defined as a “microaerophilic” bacterium.
Although it has flagella , Treponema pallidum differs from other flagellated microorganisms: in fact, these cellular appendages used for motility and called endoflagella , are located inside the bacterial cell (NOT outside, like most pathogens). The presence of endoflagella gives Treponema palliduma marked capacity for so-called “spring” movement; thanks to these particular appendages, the microorganism is able to carry out contractions, rotations, circular or “corkscrew” movements. Even the bacterial wall that covers it is particularly elastic.
Treponema pallidum CANNOT be grown on liquid or solid media: only specific serological tests can ascertain the presence of the bacterium or not.
Among the virulence factors associated with Treponema pallidum we mention:

  • hyaluronidase (hydrolytic enzyme): favors the penetration of the bacterium into the host
  • fibronectin (dimeric glycoprotein): protects Treponema pallidum itself from phagocytosis .
  • haemolysins: toxic substances produced by the bacterium

Transmission Of Infections

Being sensitive to external temperatures, bacteria of the Treponema pallidum species can only be transmitted by direct contact.
As mentioned above, Treponema pallidum is the etiological agent of syphilis, a widespread venereal disease . In addition to sexual transmission, Treponema pallidum can infect the fetus via the placenta during the last stages of pregnancy : in this case, the disease transmitted from the mother and acquired by the unborn child is called “congenital syphilis”.

The particular helical structure of Treponema allows it to move even in a viscous medium such as mucus . Once it reaches the blood and lymph , the bacterium infects tissues and mucous membranes .
In some cases, Treponema pallidum is transmitted by transfusion of infected blood.
The incubation period of syphilis ranges from 2 to 10 weeks.

Insight: clinical stages of syphilis

  1. primary phase: it is characterized by the presence of syphiloma, a highly contagious lesion that occurs at the injection site, often at the level of the external genitalia. The papule soon evolves into a hard, painful ulcer . These clinical signs appear 3-4 weeks after infection
  2. secondary stage (disseminated syphilis): after 6-12 weeks after the disappearance of the primary syphiloma, the second stage of syphilis begins. At this stage, Treponema pallidum has spread and replicated in the liver , lymph nodes , joints , muscles , skin , and mucous membranes. The characteristic signs of this phase are: widespread papules on the trunk , arms and legs, and skin sores (erosions, erythematous plaques). The affected patient often complains of fever , alopecia , thinning of the eyebrows , headache, inappetence. This phase lasts about 8 weeks, after which the patient can enter the latent ( asymptomatic ) or late (tertiary) phase.
  3. tertiary phase: it appears many years after the infection, with lesions at the level of the cardiovascular system and the CNS , associated with sores on the skin or internal organs .

Treponema pallidum infection is diagnosed by a sample of fluid extracted from a suspected ulcer. The liquid will then be evaluated under a microscope.
The doctor may also submit the patient to blood tests , looking for any specific antibodies (present in all people affected by syphilis) .
Medical statistics show that a good number of syphilis patients have a high risk of contracting HIV : for this reason, syphilitics are invited to undergo all the necessary tests to test for any concomitant HIV infection .

Prevention And Treatment Of Infections

Since there is no vaccine for syphilis, it is advisable to refrain from unprotected sex with subjects at risk; otherwise, carry out regular blood tests , as well as notify all people with whom risky relationships have been consumed, up to a year before the onset of syphilis symptoms . Treponema pallidum
infections can be treated with antibiotics such as penicillin (the drug of choice), procaine , erythromycin , doxycycline , and tetracyclines. Prevention is the best weapon to escape from Treponema pallidum infections .

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