Neisseria meningitidis
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| Neisseria meningitidis | ||||||||||||||
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| Neisseria meningitidis |
Description & Significance
Neisseria meningitidis is a type of gram negative, parasitic, aerobic bacteria included among the proteobacteria. These organisms are extremely oxidase and catalase positive, are nonmotile or endospore forming and are extremely susceptible to drying. N. meningitidis bacteria are also diplococci, and therefore resemble coffee beans somewhat in their shape. This bacteria has been found to be the causative agent of bacterial meningitis, a disease that has appeared to date back to the 16th century. However the disease was only first described in 1805 by Swiss physician Gaspard Vieusseaux. Following Vieusseaux, Italian pathologists Ettore Marchiafava and Angelo Celli also described the micrococci in a sample of cerebral spinal fluid (CSF). Finally in 1887, the bacteria was isolated by Anton Weichselbaum.
Genome
The genome of Neisseria menignitidis, as well as other bacteria, contains its DNA within which its entire hereditary information is encoded. The genome of 3 of the 13 serotypes have been sequenced. Strain Z2491, belonging to serotype A, was completely sequenced in September of 2001 by the Sanger Institute. The genome of this particular strain was found to be circular, with a nucleotide length of 2,184,406, was found to contain 2,208 genes, 2,049 protein coding genes, 72 structural RNAs, 87 pseudogenes, 1 contig, be 80% coding and have a GC content of 51%.
Strain MC58 (serotype B) was sequenced by the TIGR Center in September of 2001. It's genome was found to be circular, 2,272,360 nucleotides in length, as well as 79% coding and have a GC content of 51%. Furthermore it was found to contain 2,225 genes, 2,063 protein coding genes, 71 structural RNAs, 91 pseudogenes and no contigs. Sequencing of strain FAM18 (serotype C) was completed by the Sanger Institute in January of 2004 as well and it's genome was also found to be circular. It was 2,194,961 nucleotides in length, had 2,046 genes, 1,917 protein coding genes, 71 structural RNAs, 58 pseudogenes, no contigs, be 81% coding and have a GC content of 51%.
Clearly, the information provided by the genomic sequencing of strains Z2491, MC58 and FAM18 of serotypes A, B, and C, respectively, has enabled researches to discover the means by which this bacteria invade and infect their hosts. Furthermore, without this molecular level understanding, vaccination and treatment are not only made possible, but more efficient as well.
Cell structure and metabolism
A notable feature of this bacteria are it's prominent antiphagocytic polysaccharide capsules. The 13 known serogroups; A, B, C, H, I, K, L, M, X, Y, Z, 29E and W135; are grouped on the basis of the capsular polysaccharides which envelope them. They are then further classified into 10 serotypes on the basis of class 2 or 3 OMP antigens, as well as 10 subtypes on the basis of class 1 OMP antigens, and finally 13 immunotypes on the basis of lipooligosccharide antigens. The cell surface of Neisseria meningitidis also possesses type IV pili, which are retractile fibers that serve in their attachment to epithelial cells during host colonization and invasion. N. meningitidis also contains an outer membrane integral protein known as OpcA. This protein's purpose has been linked to cell adhesion of Neisseria meningitidis to epithelial, as well as endothelial cells via binding to vitronectin and proteoglycan cell-surface receptors located within the host. The OpcA protein has been found to function independently of pilus based adhesion, mentioned above.
As far as the bacteria's metabolism is concerned, a study conducted by Archibald and Devoe have provided insight into the dependency for N. meningitidis to metabolize iron in order to maintain cellular functioning. Other studies of the bacteria appear to point to the necessity for the obtainment of glucose, pyruvate, or lactate as a sole carbon source as well (Bart et al). Further detail on these two studies can be found below, under Current Research.
Ecology
Neisseria meningitidis is strictly found in human hosts- no animal hosts are known to exist. Due to the fact that iron reduction is key to N.meningitidis' survival and flourishment, heme iron found in human blood provides the perfect breeding ground for this bacteria. However, Neisseria meningitidis impose no detrimental affects on their hosts as long as they remain in the nasopharyngeal tract. Neisseria provide no direct benefits to their human hosts either.
Pathology
As mentioned earlier, there are approximately 13 serogroups of Neisseria meningiditis. The genes of the sequeneced serogroups have been found to undergo phase variation more so than any other pathogen studied to date. Accordingly, this ability seems to underlie the bacteria's expression and contributes to their ability to persevere over the hosts immune system response[1]]. Among these known strains, serogroups A, B, and C have been found to be those responsible for 90% of meningococcal meningitis and septicemic cases. Specifically, serogroup A has been implicated in meningitis epidemics in developing countries, while serogroups B and C have been implicated in meningitis epidemics in already developed countries.
Neisseria meningitidis is only found in human hosts of which 5-15% of the population are carriers. There is a 3-30% normal carrier state lasting days to months that provides the reservoir for infection of susceptible persons. Specifically, the bacterium can be found in the nasopharyngeal tract, in its asymptomatic form. Transformation from it's initial asymptomatic form into meningitis arises when the bacterium crosses the mucosal barrier via type IV pili, and enters the blood stream. Once in the blood stream they are free to travel to the cerebral spinal fluid or the meninges, tissues that surround the brain and spinal cord. Accordingly, this infection of the meninges results in bacterial meningitis.
Meningitis results in the swelling of the meninges and causes flu-like such as high fever, severe headache, and neck stiffness and pain that make touching your chin to your chest difficult. It is also highly contagious, easily passed to individuals via kissing, sexual contact, coughing and sneezing, giving birth and living in crowded conditions such as dormitories. Risk factors for contracting this disease include time of year (most prevalent during late winter/early spring) being male, age, genetics, a weakened immune system due to a condition such as HIV, and living in crowded conditions as for mentioned. If left untreated meningitis could result in meningicoccal septicemia[[2]] and/or death. Fortunately, antibiotics and steriod medications can be used to cure the disease and treat inflammation, respectively.
Application to Biotechnology
Research conducted on the various serotypes and strains of Neisseria meningitidis have yeilded no beneficial enzymes or compounds that are applicable to biotechnology.
Current Research
A vast amount of research is being performed on Neisseria meningitidis in order to gain further insight into a varitey of different areas. In one study, researchers have used serogroup B Neisseria meningitidis as a means of assertaining the effect that luxS has on virulence. LuxS is required for autoindicer-2 (AI-2) production. Autoinducer-2 is a boron-based molecule that is produced by bacteria, such as N. meninigitidis, that controls the signals in the quorum sensing process by which biofilms establish a network of communication between them.[[3]] Numerous bacteria have been found to posses luxS. In this particular study reseachers have discovered that serotype B Neisseris meningitidis posses a functional copy of luxS that is vital for full meningococcal virulence. Consequently, strains that lack luxS (due to a deletion) are defective to bacteremia, a precursor of meningococcal pathogenesis.[[4]]
References
http://en.wikipedia.org/wiki/Neisseria_meningitidis http://www.brown.edu/Courses/Bio_160/Projects1999/bmenin/nmenin.html http://www.sanger.ac.uk/Projects/N_meningitidis http://www.webmd.com/a-to-z-guides/meningitis-cause http://en.wikipedia.org/wiki/Genomes http://www.sciencemag.org/cgi/content/abstract/sci;287/5459/1809 http://www.cehs.siu.edu/fix/medmicro/neiss.htm http://genomebiology.com/2007/8/7/R136