User talk:DusmanK

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A Microbial Biorealm page on the genus DusmanK

Classification

Higher order taxa

Domain: Bacteria Phylum: Firmicutes Class: Cocci Order: Lactobacillales Family: Streptococcaceae

Species

NCBI: Taxonomy

Streptococcus pneumoniae

Description and significance

S. pnuemoniae is an oval, spherical bacterium called a cocci. It is about 0.5-1.25 micrometers in length and usually never stands alone. Many times it can be found in pairs or chains. It is a Gram positive bacteria that is non-motile and cannot form spores. This bacteria is a section of the nasopharangeal flora and there are more than 85 different antigenic types of S. pneumoniae. It is estimated to cause nearly 3 million deaths in children per year due to meningitis, pneumonia, and bacteremia. This bacterium is important because it is something that affects humans each year, and it is something to watch for since it is naturally present in our bodies. [1]

In 1881 the organism was first located and grown by Pasteur. Throughout this decade S. pneumoniae was considered to be a major cause of pneumonia. In 1884, the Gram stain technique was invented which allowed the specific pneumococcal pneumoniae strand to be differentiated from other strands and defined as the leading cause for pneumonia. In 1913, Lister researched a type-specific antibody associated with the bacterium. [2]

Genome structure

The genome for S. pneumoniae is comprised of 2,160,837 base pairs within a single circular chromosome. There are 39.7% GC base pairs in the genome, resulting in 60.3% AT base pairs also present. The genome was figured out by using a random shotgun sequencing technique. Researchers were able to sequence the genome by taking a clinical isolate from the blood of a 30-year-old, male patient. There are 2236 genes that comprise the genome, and of these, 1155 are situated to the right of the replication fork, and 1081 genes are located to the left. There were 1440 predicted proteins that encode for biological roles, 359 that encode for unknown function, and 437 were not able to matched. The genome is also rich in insertion sequences, which comprise of about 5% of the genome. [3]

Cell structure and metabolism

The bacterium is completely surrounded by a capsule made up of polysaccharides. There have been 90 different types of capsules identified for S. pneumoniae, which results in the high amount of antigenic strands of the bacteria. The bacterium is also protected by a cell wall, which is at least six layers thick. It is composed of peptidoglycan, like all bacterial cell walls, and there is a presence of techoic acid that is attached between every third N-acetlymuramic acid. There is also lipoteichoic acid present in the cell wall, which is chemically the same as teichoic acid. These two acids together are essential in the chemical make up of the cell because they allow S. pneumoniae to adhere to choline-binding receptors that are located on almost all human cells. [4]

Abundant amounts of pili have been associated with many different strains of S. pneumoniae. Pili are hair like structures that project out of the surface of the bacterial cell. These pili help the bacterial cells colonize in the upper respiratory tract, their main site of infection. There are also approximately 500 different types of surface proteins that may be present on pneumococcus cells. Some of these proteins are only associated with the cell wall, while others are membrane associated. Some of the cell wall associated proteins include five different penicillin-binding proteins (PRPs), an IgA protease, and two neuroaminidases. There are also choline-binding proteins (CBPs) that are attached to the outer membrane of the bacterial cell. [4]

Interestingly, the bacteria grows an enzyme (autolysin) which gives it the capability to autolyse if needed. When the culture of bacteria grows to stationary phase, this autolysin allows for the entire culture to lyse killing it all. Usually this lysing occurs between 18 and 24 hours after optimal growth. [4]

Ecology

Streptococcus pneumoniae is present in human’s natural flora in the respiratory tract. At normal levels, the bacterium has a positive effect on the body and is beneficial. However, if levels of the bacterium increase infection may occur. [4]

In lab, S. pneumoniae is usually grown in cultures with agar that contains blood. This is because on this blood agar, the colonies are able to form a zone of hemolysis which separates S. pneumoniae from another type of bacteria that also lives in the respiratory tract. This other bacteria is Streptococcus viridans. [4]

Pathology

There are many different types of infections that S. pneumoniae causes in humans. These include pneumonia, meningitis, otitis media, conjunctivitis, pericarditis, and arthritis. One of the most commonly caused diseases from S. pneumoniae is pneumonia. This bacterial is naturally apart of the human flora in the respiratory tract. However, at high levels the bacteria may cause what is known as strep pneumonia or pneumococcal pneumonia. Depending on the strain of bacteria, the induced pneumnia can have a fatality rate up to 30% of patients diagnosed. [5]

Once this bacteria is embedded in the lung macropahges and neutrophils have a hard time engulfing the bacteria in order to get rid of it because of the surrounding protective capsule. Researchers found that some strains of S. pneumonia were much more pathogenic than others, and the attributed this to the fact that the strains had different capsule build ups. This is related to the type of glycoproteins and polysaccharides that make up the capsule. Many of the infections that S. pneumoniae causes occur in fluid filled areas. The pili attached to the surface of the bacterial cells help to anchor the bacterial cell into place. [5]

Current Research and or Application to Biotechnology

There has been much research on Streptococcus pnemoniae. More recently, researchers have found that the bacteria is able to break down mucus membranes and this is how it infects different parts of the body. Researchers from the Schepens Eye Research Institute studied this bacteria because it causes conjunctivitis of the eye, or in lamens terms pink eye. The researchers hypothesized that these non-opportunistic bacteria must have a way to remove mucins in the mucus membrane in order to make an opening for them to enter and infect. In order to test their hypothesis they grew the bacteria in a culture and then applied it to cells imitating the membrane of the eye to see the effect. They found that the mucins that were anchored to the membrane were cut off by the bacteria creating openings for the bacteria to enter. In order to determine the responsible enzyme present in the bacteria the researchers used mass spectrometry. They found the enzyme ZmpC to be the cause and they confirmed this by deleting the enzyme from the bacteria and seeing if the “new” bacteria had any effect on the membrane. They found that without ZmpC there was no effect. [6]

There has been an increase in resistance to S. pneumoniae over the last century. This resistance started in other countries, however, resistance in the United States is starting to increase. This increase in resistance to different drugs has made it very difficult for physicians to treat the bacteria. Whitney et al. studied data on invasive pneumococcal disease in patients between 1995 and 1998. They found that out of all the different strains of the bacteria introduced, 24% of these strains were resistant to penicillin. These strains that were resistant to penicillin are more susceptible to be resistant to other antimicrobial drugs [7].

Marion et al. conducted a research study in which they wanted to study how Streptococcus pneumoniae is able to utilize different sources of hyaluronic acid for growth. It has been hypothesized that this type of bacteria uses carbohydrates to grow, however, the lack of carbohydrates in the respiratory tract leads researchers to believe that the bacteria must use some type of complex glycan structures. The researchers found that when hyaluronate lyase (Hyl) cleaves hyaluronic acid into a number of disaccharides, the bacteria use the carbohydrates that are released from this reaction in order to grow [8]. This is just one way in which this bacteria may grow; more research is crucial in order to determine other mechanisms the bacterium uses to survive.

References

[1] Bergey, D. H. Bergey's Manual of Systematic Bacteriology. Vol. 3. New York: Springer, 2001.

[2] "Streptococcus Pneumoniae Infections: Microbiology, Epidemiology, Treatment, and Prevention." Medscape Education. Medscape. Web. 9 May 2012. <http://www.medscape.org/viewarticle/451448>.

[3] Tettelin, Herve. Et al. "Complete Genome Sequence of a Virulent Isolate of Streptococcus Pneumonia." ScienceMag. Science AAAS, 20 July 2001. Web. 9 May 2012. <http://www.sciencemag.org/content/293/5529/498.full.pdf>.

[4] Todar, Kenneth. "Streptococcus Pneumoniae and Pneumococcal Pneumonia." Streptococcus Pneumoniae and Pneumococcal Pneumonia. Web. 09 May 2012. <http://textbookofbacteriology.net/S.pneumoniae_2.html>.

[5] "Streptococcus and Associated Pathology." Streptococcus and Associated Pathology. Community College of Indiana. Web. 09 May 2012. <http://faculty.ivytech.edu/~twmurphy/text_pg/strep.htm>.

[6] "How a Bacterial Pathogen Breaks Down Barriers to Enter and Infect Cells." ScienceDaily. ScienceDaily, 08 Mar. 2012. Web. 14 Mar. 2012. <http://www.sciencedaily.com/releases/2012/03/120308101623.htm>.

[7] Whitney, Cynthia, Et al. "The New England Journal of Medicine." Increasing Prevalence of Multidrug-Resistant Streptococcus Pneumoniae in the United States”. 28 Dec. 2000. Web. 09 May 2012. <http://www.nejm.org/doi/full/10.1056/NEJM200012283432603>.

[8] Marion, Carolyn, Et al. "American Society for MicrobiologyInfection and Immunity." Streptococcus Pneumoniae Can Utilize Multiple Sources of Hyaluronic Acid for Growth. 6 Feb. 2012. Web. 09 May 2012. <http://iai.asm.org/content/early/2012/01/30/IAI.05756- 11.short>.

Edited by student of Dr. Lynn M Bedard, DePauw University http://www.depauw.edu