Treponema pallidum

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Treponema Pallidium
Scientific classification
Phylum: Spirochaetes Order: Spirochaetales Family: Spirochaetacae Genus: Treponema Species: T. pallidium

Description and significance

Treponema pallidum is a spirochete bacteria that has two subspecies that cause human disease. These are T. pallidum pallidum, which causes venereal syphilis; and T. pallidum pertenue, which causes yaws. Both of these subspecies are members of the family, Spirochaetales, which also incudes the spirochetes Leptospira, the casue of the human disease, leptospirosis, and Borrelia, a genus of several species of spirochetes that cause the human diseases of relapsing fever and Lyme disease. Treponema pallidum is an unusual bacterium that is particularly parasitic. It lacks the enzymes of the Krebs cycle and oxidative phosphorylation, and transports many nutrients and structural substrates, such as amino acids and sugars, into its cytoplasm from its environment. This is one reason that the organism cannot live outside its host's body for any appreciable length of time and why infections must be transmitted through close contact.

Pathogenic subspecies of Treponema pallidum are very difficult to culture in the laboratory. Unlike most other bacteria that colonize and infect the human body, even special techniques for culture on artificial media are unsuccessful for the routine identification of these organisms. Instead, classically, dark field examination of a body fluid containing a large number of these spiral shaped motile bacteria was required for laboratory identification. More recently, PCR techniques are able to distinguish the organisms; this is especially helpful because both of the two subspecies of Treponema pallidum, as well as other harmless species of Treponema look identical or similar under darkfield exam.

Genome structure

Treponema pallidium is a prokaryote with one of the smaller genomes. The organism has many processes that are similar and required for other organisms although it is dependent on the host for its survival. Like other eukaryotes it undergoes transcription, translation, replication, repair and has restriction- modification systems. Its genomic sequence is very close to that of Borrelia burgdorferi that causes lyme disease in humans. The total genome sequence of the organism has 1,138,006 base pairs. The number of base pairs of the predicted coding sequences or of the number of open reading frames is 1041.

Inorder to repair DNA the T. Pallidium goes through methods such as uvr exision repair, mutL/mutS mismatch repair, mut Y and dat.

It lacks type 4 topoisomerase that is involved in the process of chromosome segregation. Chromosome segregation in T. Pallidium is able to occur by another mechanism that involves binding hemimethylated DNA to the cytoplasmic membrane. The spirochete T. Pallidium encodes for the homologs that are of the recF pathway thatare involved in recombination.

Cell structure and metabolism

IT has an outer membrane a cytoplasmic membrane and it also consists of a thin peptidoglycan layer. Its outer membrane has relatively fewer integral membrane proteins. This permits the organism to evade the human response from the immune system.

The energy source for T. Pallidium are mainly carbohydrates like glucose, galactose and glycerol. In tissue culture system the growth and multiplication of T. Pallidium is only due to glucose, mannose and maltose. This has been an suggested due to experimental evidence. The T. Pallidium has all the genes that code for enzymes that are required for the glycolytic pathway. T. Pallidium has homologs of the enzymes phosphofructokinase and pyruvate kinase that are there in eubacterial organisms which use pyrophosphate for energy metabolism. It does not have any of the genes that code for substances required in the tricarboxylic acid cycle or of oxidative phosphorylation.

T. Pallidium does not have a respiratory transport electron chain. ATP is therefore formed by substrate level phosphorylation and so the membrane potential is created by the reverse reaction of the enzyme ATP synthase. The ATP synthase in the T.Pallidium is of the V1V0 type. It also has two operons of the V1V0 type and each contains seven genes.

Pathology

T. Pallidium is the causative agent of syphilis. The organism is microaerophile which means it requires little oxygen. It is transmitted through humans and cause diseases and finally affects the nervous system. It is only transmitted sexually. It can be transmitted from mother to baby. The disease it transmitted by sexual contact and it does not spread by using things that are used by others for regular purposes such as clothes, utensils, etc. The disease is spread from one person to another by contact with syphilis sores. It is spread through contact with syphilis sores that are caused by the organism. The sores can occur on the external anus, vagina, and internal anus and can also occur in the rectum. The primary stage of syphilis there is a chancre that is round and does not cause pain. It heals on its own and if the disease is not treated it will go into the secondary and late phases. The sores can also occur in the mouth. Sometime it is possible for a person to know whether the person has syphilis because sores occur in inside of the vagina and anus in males and females. So the person should be tested for syphilis. The secondary phase is associated with rash through out the body. If it is not treated the symptoms will go into the latent phase and it can cause damage to organs and it affect the coordination and affect the important organs and may even lead to death.

References

Sheila A. Lukehart. Chapter 153. "Syphilis" in Dennis L. Kasper, Eugene Braunwald, Anthony S. Fauci, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Kurt J. Isselbacher, Eds.Harrison's Principles of Internal Medicine, 16th Edition