Mycoplasma gallisepticum
| Mycoplasma gallisepticum | ||||||||||||
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Mycoplasma gallisepticum |
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| Scientific name | ||||||||||||
| Mycoplasma gallisepticum | ||||||||||||
| Edward & Kanarek 1960 |
Mycoplasma gallisepticum (MG) is a prokaryote from the class of the Mollicutes and the family of the Mycoplasmataceae and lives in the upper respiratory tract. MG differs from bacteria in that it lacks a cell wall . The genome of this species was completely sequenced in 2012.
Occurrence
Mycoplasma gallisepticum occurs as a causative agent of respiratory diseases in poultry, e.g. B. chickens and turkeys and can be isolated from their respiratory tract . The infection often results in a mixed infection with other viral or bacterial pathogens.
features
Species of the genus Mycoplasma (also known as mycoplasma ) have the peculiarity that they do not have a cell wall that is otherwise typical for bacteria . This makes them more like a protoplast , which is also evident in the cell morphology: They are of diverse (pleomorphic), variable, vesicular shape. They grow aerobically to facultatively anaerobically , and although they are shown as Gram- negative in a Gram stain because they lack the cell wall, genetic studies have shown that they are related to Gram-positive cocci with low GC content in the DNA .
Due to the lack of a murein layer , the cells are susceptible to osmotic fluctuations in the surrounding medium, but are less labile compared to a protoplast. This is due to the presence of sterols in the cytoplasmic membrane , so Mycoplasma gallisepticum needs cholesterol (cholesterol) in the medium in order to be able to grow. But since they normally colonize a host organism as parasites, they receive sterols and other essential metabolic components from its cells. In addition, lipoglycans are found in the cell membrane, as can also be found in the Thermoplasmatales , an order within the archaea . They enable the bacterial cells to attach to the cell surface receptors of animal host cells in a similar way to the lipopolysaccharides of the gram-negative bacteria.
metabolism
Like all representatives of this genus, Mycoplasma gallisepticum is to be regarded as a “metabolic cripple”. In the course of evolution, the bacterium has lost many non-essential genes, on the one hand those for the formation of a cell wall, but also those for the synthesis of many metabolic products that it has received from the host cells. This can also be seen in the very small genome of this species, which has just 986 kilobase pairs (kb), which is less than a fifth of the genome size of Escherichia coli . It either has to obtain the necessary metabolic components from the host cells or they have to be added to the nutrient medium .
proof
When isolating the pathogen, it should be noted that due to its properties, it cannot survive long in the environment. B. Store swabs of infected tissue in sterile nutrient solution with a swab to protect cells from desiccation.
On solid culture media containing agar-agar , Mycoplasma gallisepticum forms colonies that resemble a fried egg. This typical appearance is due to the fact that the cells grow so that they are embedded in the medium. If you want to grow them on a nutrient medium, common complete media for bacteria are not sufficient, because their small genome size means that they have lost the ability to synthesize numerous metabolic components. The cultivation of M. gallisepticum is therefore laborious because very complex nutrient media have to be used, e.g. B. a yeast extract-peptone-beef heart infusion medium, which also contains fresh serum to cover the need for sterols and unsaturated fatty acids .
The detection of an infection with Mycoplasma gallisepticum is therefore mostly carried out by detecting the antibodies formed in the infected organism with the help of the ELISA method; a real-time multiplex PCR test kit is also permitted to directly detect the DNA of the bacterium.
Veterinary importance
Sources of Infection and Infectious Diseases
The infection is considered to be the conditioner of the CRD (Chronic Respiratory Disease), which gives an overall clinical picture through secondary pathogens. Infection by Mycoplasma gallisepticum in domestic chickens occurs as a smear infection via the housing equipment, as a droplet infection and directly by the hen on the embryo. The disease ( mycoplasmosis ) usually manifests itself as an initially dry, short sneeze, which is expelled through the nostrils with the beak closed. With a progressive spread in the respiratory tract, clear discharge from the nostrils can also be seen in the form of a moist film towards the tip of the beak. This film is particularly noticeable when leftover food and litter stick around the openings.
In turkeys, the symptoms are e.g. Sometimes similar and are referred to as infectious sinusitis , but changes in joints and thus motor functions have also been described.
Although M. gallisepticum can only survive in the environment for a short time, the pathogen is able to quickly transfer itself to a new host. Factory farming in poultry farming favors this. The extent to which wild birds in contact with infected animals act as vectors for the transmission of Mycoplasma gallisepticum in poultry farming still needs to be investigated .
Pathogenicity
The pathogenicity of mycoplasma has not yet been adequately clarified; it is assumed that the lipoglycans contained in the cell membrane are involved, as they trigger the production of antibodies in test animals. M. gallisepticum can attach to the animal cells of the target tissue, invade them and remain intracellular. In addition, they are able to change the three-dimensional structure of their surface antigens . It is assumed that this mechanism bypasses the host's immune response in order to survive in the host. The exact processes at the cellular and molecular level that lead to the clinical symptoms are still unclear, it is likely that the pathogenic structures of the cell membrane act as endotoxin , they are released after the cell is destroyed. These toxins are deposited in the respiratory tract and thus make the animal usable for consumption to a limited extent.
therapy
A rehabilitation of the affected population is only possible by interrupting the chain of infection through a sufficiently long stabling. Mycoplasma gallisepticum reacts to the antibiotic tylosin . The symptoms can thus be suppressed for a short time, but reinfection occurs promptly if the stable is continuously occupied, as the bacterium outside the body in the environment (stable, exercise area) maintains its ability to infect for a limited time. The occurrence of symptoms facilitates the infection by other economically important respiratory diseases such as B. Infectious bronchitis (IB) and avian rhinotracheitis (ART).
In Austria, efforts are being made, which are being strengthened by research work at the University of Veterinary Medicine in Vienna, to get poultry flocks free of Mycoplasma gallisepticum through targeted stable management . The reason is the suspicion of zoonoses . For example, the bacterium is said to cause irritation of the conjunctiva ( conjunctivitis ) in humans .
swell
- Klaus Damme, Ralf-Achim Hildebrand: Poultry farming . Ulmer 2002, ISBN 978-3800139293
- Lecture by Detlef Bibl as part of the veterinary training at Vet.med. Univ. Vienna
Individual evidence
- ↑ a b Mycoplasma gallisepticum on the website of the Genoms Online Database (GOLD). Retrieved March 2, 2013 .
- ^ Annual report of FLI 2005 (PDF; 2.8 MB) of the Friedrich Loeffler Institute , accessed on March 2, 2013.
- ↑ a b c d Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 .
- ↑ a b Herbert Hof, Rüdiger Dörries: Dual Series: Medical Microbiology. 3. Edition. Thieme Verlag, Stuttgart 2005, ISBN 978-3-13-125313-2 .
- ^ A b c J. M. Bradbury: Gordon Memorial Lecture. Poultry mycoplasmas: sophisticated pathogens in simple guise. In: British poultry science. Volume 46, Number 2, April 2005, pp. 125-136, ISSN 0007-1668 . PMID 15957431 . (Review).
- ↑ List of the means approved according to § 17 c TierSG (PDF; 67 kB) of the Friedrich-Loeffler-Institut , accessed on March 2, 2013
