Mycobacteria

​​ //**__Mycobacteria __**// Author: Megan McTaggart Thursday, May 20, 2010

**__Abstract__**
This presentation emphasizes the genus Mycobacteria, with specific emphasis being placed on //Mycobacterium tuberculosis//. Mycobacteria is generally found in aquatic or moist environments and is most known for the disease causing species, //Mycobacterium tuberculosis// and //Mycobacterium leprae.// Characteristics of mycobacteria are listed within the presentation as well as distinctive features of the mycobacterium cell wall that help to distinguish it from many other bacterial species. The Ziehl-Neelseen acid fast staining procedure is discussed in terms of how it is useful in identifying and defining different species of mycobacteria, as well as how the process penetrates the thick cell wall of mycobacteria. The presentation emphasizes //Mycobacterium tuberculosis//, listing several charactersitics of the species useful in identifying it. The BCG vaccine is also discussed within the presentation and how the vaccine is not widely recommended within the United States.

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After taking a semester of microbiology and briefly learning about some of the various species of bacteria and how they are responsible for diseases, I decided to do further research on the particular bacteria that was responsible for causing Tuberculosis disease. In my research, I discovered that the //Mycobacterium tuberculosis// complex was the main factor behind the Tuberculosis disease and consisted of four specific species of mycobacteria. The //Mycobacterium// genus is most often known and studied for //Mycobacterium tuberculosis// and //Mycobacterium leprae//. However, as I discovered, there are nearly seventy different species of mycobacteria and a majority of the species are not harmful or disease-causing. In fact, most mycobacteria are referred to as MOTTS and are actually environmental organisms (Steyn, 1999). Another interesting characteristics of mycobacteria is their distinctive cell wall which includes a thick, hydrophobic layer with a high lipid content (Steyn, 1999).======

**__Discussion __**

 * __What are mycobacteria?__**
 * Mycobacteria are generally found in aquatic environments or environments where there is moisture. Very few sepecies of mycobacteria are responsible for causing disease in animals and/or humans. There are over seventy different species of mycobacteria that are presently known. The two most common forms are: //Mycobacterium tuberculosis// and //Mycobacterium leprae//. All other species of mycobacteria are considered to be environmental organisms and are often referred to as MOTTS, which stands for Mycobacteria other than Tuberculosis (Steyn, 1999). The taxonomy of mycobacteria is as follows:
 * __Order:__ Actinomycetales
 * __Family:__ Mycobacteriaceae
 * __Genus:__ Mycobacterium


 * __Characteristics of Mycobacteria:__**
 * rods
 * known as "acid-fast bacilli"
 * gram-resistant
 * non-motile
 * obligate aerobes
 * facultative intracellular pathogens
 * non-endospore forming
 * acid fast
 * generally resistant to drugs and chemical biocides
 * Mycobacteria are the third most resistant form of mircroorganisms, falling just below prions and endospores of bacteria.
 * have a cell wall that is similiar to gram negative bacteria
 * hydrophobic
 * resistant to chemical antimicrobials used as antiseptics and disinfectants




 * __What is makes the cell wall of mycobacteria so unusual and distinctive?__**
 * The cell walls of mycobacteria are often referred to as being waxy, hydrophobic, and having a high lipid content. In mycobacteria, the outermost lipopolysaccharide layer is replaced with mycolic acids, forming a waxy, water-resistant layer. This layer makes the bacteria resistant to drying and prevents antimicrobial drugs from being able to enter the cell. The type of mycolic acids present in the cell wall are used to distinguish different mycobacteria. Nutrients enter the cell by passing through the waxy, water-resistant layer slowly which contributes to the slow growth rate of mycobacteria (Steyn, 1999).


 * __Ziehl-Neelsen (Acid-Fast) Stain__**
 * This stain is a differential staining technique used to identify specific strains of mycobacteria. Heat and phenol (carbolic acid) are used to help penetrate the dye through the thick cell wall and into the mycobacterial cells. The use of heat and phenol (carbolic acid) is necessary because basic dyes used in Gram Stains are impermeable due to the high lipid and wax content of the cell wall.This particular stain is effective in diagnosing tuberculosis and leprosy, which are caused my //M. tuberculosis// and //M. leprae// (Shoeb, 2005).


 * __What is the //Mycobacterium tuberculosis// Complex?__**
 * The //Mycobacterium tuberculosis// complex consists of four different species of mycobacterium, all of which are known to cause the disease, Tuberculosis. The four species are//: Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis//, and //Mycobacterium microti.// Recently, //M. africanum, M. bovis,// and //M. microti// were considered to be sub-species of //M. tuberculosis// (Steyn, 1999)//.//


 * __Characterisitics and Morphology of //Mycobacterium tuberculosis://__**
 * An obligate pathogen that can infect a wide variety of animals and utilizes man as the principal host
 * Slender, straight or slightly curved bacilli
 * Non-motile and non-encapsulated
 * Aerobic
 * Slow growing, dividing every 18-24 hours
 * Sensitive to UV light and heat from pasteurization
 * Resistant to chemical disinfectants and drying agents
 * Infects alveolar macrophages

The BCG vaccine is a vaccine that was developed to prevent tuberculosis (TB) disease. It is often given to foreign-born individiuals, where there is a high prevalence of TB (BCG Vaccines, 1996). This is done in order to prevent childhood tuberculosis, meningitis, and miliary disease. The vaccine is a live vaccine, derived from a strain //of Mycobacterium bovis//. It was first administered to humans in 1921. The vaccine is not recommended within the United States due to the low prevelance of TB and the lack of effectivness demonstrated during clinical trials (CDC, 2008).
 * __Bacille Calmette-Geurin (BCG) Vaccine:__**



**__Literature Cited:__** BCG Vaccines. (1996, April 26). //MMWR: Morbidity and Mortality Weekly Report//. Retrieved May 18, 2010, from []

CDC | TB | Fact Sheets - BCG Vaccine. (2008,Nov.). //Centers for Disease Control and Prevention//. Retrieved May 19, 2010, from []

Case, C. L., Funke, B. R., & Tortora, G. J. (2009). Chapter 7: The Control of Microbial Growth. //Microbiology: An Introduction (10th Edition)// (10 ed., p. 203). San Fransisco:Benjamin Cummings.

Shoeb, H. (2005, March 11). MicrobeLibrary - Acid-Fast (Ziehl-Neelsen) Stain. //Microbe Library: teaching resource includes images, animations, videos, articles and reviews for undergraduate biology and microbiology education about the microbial world.//. Retrieved May 20, 2010, from []

Steyn, L. (1999, March 12). Mycobacterial Diseases. //University of Cape Town / Welcome//. Retrieved May 17, 2010, from h[|ttp://web.uct.ac.za/depts/mmi/lsteyn/lecture.html]

Steyn, L. (1999, March 12). Tuberculosis. //University of Cape Town / Welcome//. Retrieved May 18, 2010, from []