Mycoplasma bovis
A Microbial Biorealm page on the genus Mycoplasma bovis
Classification
Higher order taxa
Cellular organism, Bacteria, Firmicutes, Mollicutes, Mycoplasmatales, Mycoplasmataceae,Mycoplasma
Species
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NCBI: Taxonomy |
Mycoplasma bovis
Description and significance
Mycoplasma bovis is the most pathogenic bovine mycoplasma in Europe and North America, causing a significant cause of bovine pneumonia, mastitis, arthritis, genital disorders, and abortion. The completion of genome sequence of M. bovis is still in progress by TIGR and Univ. of Missouri-Columbia. It is very important to have its genome sequenced because it has ability to survive in such an extreme environment and the causes of hugh economical losses in cattle and milk production in both Europe and the USA. The losses caused by respiratory diseases in cattle is approximately a sum of 576 million Euros per year in Europe. M. bovis is estimated to be responsible for at least for the quarter or third of these losses. In the USA, this organism causes a loss of $32 million per year as a result of the loss of the weight gain and the diminished carcass value. The expenses due to M. bovis mastitis are estimated to be $108 million per year (10). Mycoplasma bovis was first isolated in the USA from the milk of a mastitic cow. due to the similar picture tothe contagious agalactia of sheep caused by M. agalactiae it got the name Mycoplasma bovimastitidis then Mycoplasma agalactiae subsp. bovis(10). Late following the examination of the 16S ribosomal RNA it was elevated to species rank and received the name Mycoplasma bovis. The global transportation of animals and sperm made this to be spread out to numerous countries(7).
Genome structure
The Mycoplasma bovis genome structure continues to undergo research. M. bovis is very similar to M. agalactiae in many aspects. The 16S RNA sequence shows only 8 nucleotides difference between these speices. The sequencing of the uvrC gene also revealed differences. In comparison of pulsed field gel electrophoresis profiles, the estimated genomic size of M. bovis was 961±18, 9 Kbp while M. agalactiae has 945±84 Kbp. It has a low G+C ratio of 27.8-32.9 mole% (14).
Cell structure and metabolism
Mycoplasma bovis is similar to Mycoplasma agalactiae in biochemical properties as it does not ferment glucose and hydrolyse arginine. However, it uses organic acids, lactate and pyruvate as energy sources for its growth. The film and spot formation can also been seen on the surface of solid media indicating the possession of lipolytic activity (12). The genus Mycoplasma is known as self-replicating organism and phylogenetically related to gram-positivie eurobacteria. M.bovis lacks a cell wall, periplasmic space, and contains a small genome (4,6). M. bovis was recently shown to possess a family of phase- and size-variable membrane surface lipoprotein antigens (Vsps). These proteins spontaneously undergo noncoordinate phase variation between on and off expression states, generating surface antigenic variation. The spontaneously high rate of Vsp phenotypic swithcing involves DNA reaarangements that occur at high frequency in the M. bovis chromosome. The on-off switching mechanism, the genomic organization and the structural features of the vsp genes has not yet been described (4,6).
Ecology
Mycoplasma bovis is faily susceptible to the environment. However, it is documented that M. bovis is able to survive for up to two months at 4°C in milk, for over two weeks in water, for 37 days in manure, for 2 days on wood and steel, and for 7 days on rubber and glass. M. bovis can be found in both the upper respiratory and reproductive tracts in both young and old cattle (3). M. bovis is frequently associated with other pathogenic microorganisms such as BRSV, PI-3, bovine adenoviruses, BVDV, Pasteurella multocida, Mannheimia haemolytica, Arcanobacterium pyogenes, Haemophilus sommus, Mycoplasma dispar, Mycoplasma canis and Ureaplasma diversum. These usually change the clinical picture caused by M. bovis (13).
Pathology
Mycoplasma bovis is a bacteria-like organism that causes persistent, chronic infections in calves and cows. Diverse clinical manifestations, such as mastitis in cows and arthritis and pneumonia in young animals, genital disorders, abscess, conjunctivitis, otitis, and meningitis are possible infections due to M. bovis (1).The symptoms observed from infected calves are fever, depression, loss of appetite, hyperventilation, dyspnoea, nasal discharge and coughing. The mechanisms of the pathogenesis of M. bovis are still unknown, but it uses complex strategies to invide the host organism. It adheres to the neutrophils and the macrophagesis, persisting and multipling on the surface of these cells.
Application to Biotechnology
Recently, researchers discovered that the antigenic repertoire of the M. bovis cell surface was found to be subject to rapid changes due to the presence of a set of antigenically and structurally related variable membrane surface lipoproteins designated Vsps (6). Three members, VspA, VspB, and VspC, have been been characterized and each Vsp was shown to possess the following features: independent high-frequency phase variation between ON and OFF expression states, independent high-frequency size variation, membrane anchorage via the N-terminal domain and a C-terminal region which is surface exposed, extensive repetitive domains over the full length of the Vsp molecule, and regions of shared epitopes (6). The extensive Vsp phenotypic switching in M. bovis was recently shown to be linked with high-frequency chromosomal rearrangements that occur within the vsp genomic locus. However, the genomic organization and the structural features of the vsp genes have not yet been described, nor has the precise nature of the vsp ON-OFF switching mechanism (6). The biological function of Vsp antigens in M. bovis is not yet understood. Recent date indicated an escape mechanism based on modulation of the expression of certain variable proteins to evade opsonization of specific antibodies, which can be regarded as part of the strategy of the pathogen for subverting the host defense system in response to the presence of cognate antibodies (5). Currently no vaccine is available. Preventative measures to limit infection and culling of shedders are used for controlling M. bovis. The most commonly used method of diagnosing M. bovis is detection by culture. However, it is very time consuming. A new technique, called a nested polymerase chain reaction, allows for rapid testing of preservative-treated milk. It uses DNA hybridization probes and PCR assays. This method is fast, specific, and very effective to detect M. bovis carriers in dairy herds and could save money by eliminating the need for additional individual cow milk samples (2).
Current Research
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References
Edited by student of Rachel Larsen
