Proteus OX-19 is one of the somatic antigens produced by the bacteria Proteus vulgaris. An antigen is a molecule foreign to the body that the system recognizes as a threat, generating an immune response in the form of antibodies..
Proteus vulgaris It has an antigenic structure formed by a somatic O antigen, a flagellar H and a superficial K antigen. Variants of the somatic O antigen present in this bacterium are OX-2, OX-3 and OX-19.
The OX-2 strain reacts with the species of Rickettsia, a genus of bacteria that cause spotted or spotted fevers (with the exception of Rocky Mountain spotted fever).
Meanwhile, the cells of Proteus OX-19 react in the serum of people infected with the species of Rickettsia that cause typhus and Rocky Mountain spotted fever.
This similarity between the antigenic structure of Proteus OX-19 and the one that presents Rickettsia prowazekii, attaches great importance to it in the diagnosis of epidemic typhus.
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Proteus antigen OX-19 originates from a strain of Proteus vulgaris, a facultative anaerobic, gram-negative, bacillus-type bacteria. It has numerous peripheral flagella (perotrial flagella), which gives it great mobility..
It belongs to the phylum Proteobacteria, class Gamma Proteobacteria, order Enterobacteriales, family Enterobacteriaceae. It inhabits the intestine of humans and other animals. It can also be found in free life on the ground.
Although it is of low pathogenicity, it causes some diseases, especially urinary tract infections and diarrhea. It has also been indicated as a cause of respiratory system disorders.
This bacteria grows and multiplies quickly and easily at room temperature. These are properties that make it interesting for laboratory studies..
Since the 1940s, it has been known that when cultivating Proteus vulgaris strain OX-19 in the presence of non-lethal doses of penicillin, it develops fantastic forms that are known as "large bodies".
This property of assuming different forms inspired the name of the genre Proteus. Gustav Hauser (1856-1935) proposed it in honor of Proteus, the Greek god son of Poseidon, who was capable of transforming himself into a variety of monsters.
The medical importance of the antigenic group Proteus OX19 consists in that it is used in laboratory tests to diagnose typhus, through the Weil-Felix test.
During World War I, Edmund Weil and Arthur Felix, two Austro-Hungarian scientists, discovered that Proteus OX19 generated an identical reaction that Rickettsia prowazekii (causal agent of typhus) to the human immune system.
Therefore, if a person is sick with typhus, his body produces antibodies that react to the antigens of Rickettsia prowazekii.
If we take serum from that person's blood and mix it with Proteus OX19, a precipitate or agglutination will be obtained. This is because both organisms have similar antigen groups..
Typhus is a disease caused by bacteria Rickettsia prowazekii, an obligate intracellular parasite. This bacteria is transmitted by the louse (Pediculus humanus), which contracts it by biting a sick person, being able to infect a healthy host by defecating on its skin at the time of the bite.
The infected person maintains the bacteria for life, which can multiply under conditions of depressed immune system.
Typhus symptoms include severe headaches, sustained high fever and prostration, bronchial disease, cardiovascular disorders, bleeding at different levels, mental confusion, and stupor..
On the fifth day the rash appears (skin rash all over the body except the soles of the feet and palms). This rash is maculopapular (discolored patches of skin and small bumps). Neurological complications and even coma can occur.
The Weil-Felix (WF) test is based on the fact that various species of Proteus have receptors for antibodies of the immune system, equal to those present in members of the genus Rickettsia. The only exception is the species Rickettsia akari.
The Weil-Felix agglutination test is not very sensitive and can frequently give false positives, so it is not considered a reliable test. However, the use of the Weil-Felix test is acceptable in conditions where definitive investigations are not possible..
The test must be interpreted in the correct clinical context. That is, the patient's symptoms must be taken into account and if he comes from a region where typhus is known to exist.
In addition to other general information such as trips to endemic areas, contact with reservoir animals, camping history and professional environment.
In basic terms, the test consists of the following steps:
1- The serum is extracted from the blood of the patient with rickettsiosis by centrifugation.
2- Prepare an extract of fresh cells from Proteus vulgaris OX-19 (or the commercially ready antigen is used).
3- In an agglutination tube, prepare a mixture of 0.5 ml of serum and 0.5 ml of antigen, in a battery of dilutions.
4- They are incubated at 37 ° C for two hours and left in the refrigerator until the next day at 8-10 ° C.
5- The degree of agglutination that occurs is recorded. In a complete agglutination a precipitate separates and the supernatant liquid should be totally clear.
There is also a variant in a slide (a rectangular sheet of glass measuring 75 by 25 mm and approximately 1 mm thick).
In this case, a drop of blood from the patient's finger is applied to the slide and a drop of concentrated and preserved solution of Proteus vulgaris OX-19. The result is read with the naked eye according to the intensity and speed of the agglutination.
The slide test is designed for mass examination under field conditions. The results appear to be favorably comparable to those obtained in agglutination tube tests..
Values between 1:40 and 1:80 are considered negative, while results between 1: 160 (in endemic or epidemic areas) and 1: 320 (in isolated areas) can be considered positive..
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