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The virulence (Wilson et al. 2002) or the degree to which a bacterium can cause disease to human is aided by the production of exozymes or extracellular enzymes and related substances. These enzymes have the ability to dissolve or create blood clots and to destroy materials that bind cells together and among other functions. Enzymes produced by bacteria can be grouped into 5 basic types: coagulases, kinases, hyaluronidase, collagenase and proteases. This article briefly discusses each of them separately.
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Coagulases produced by bacteria initiate the clotting of blood fibrinogen inside the blood vessels of human. The liver produces the plasma protein fibrinogen which is easily converted to fibrin through the chemical action of coagulase; note that fibrin is composed of threads that form blood clot. The bacteria can use the fibrin clot to cover themselves in such a way that they are protected from the immune defenses of human. For example, macrophages couldn’t easily engulf or phagocytose bacteria covered with fibrin clots making the bacteria survive and proliferate. Species under the genus Staphylococcus are good examples of bacteria that produce coagulases. (Konopka and Gedney 2003; Wilson et al. 2002)
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The human body has this physiological mechanism to isolate an infected portion of a body (say fingers) from the rest of the body by creating temporary blood clots which block the movement of bacteria toward the other parts of the body (Wilson et al. 2002; Lehman 2003). Unfortunately, some strains of bacteria produce kinases that dissolve the blood clots allowing them to be released from the site of infection. Widely known bacterial kinases include the staphylokinase produced by staphylococci (e.g. Staphylococcus aureus) and the streptokinase (a.k.a fibrinolysin) produced by streptococci (e.g. Streptococcus pyogenes). Interestingly, bacterial kinases have promising application in medicine because it was experimentally demonstrated, that they have successfully dissolved some kinds of blood clots in coronary arteries; they could therefore help heart attack victims.
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Cells in the connective tissues of humans are joined together in place by hyaluronic acid, a special kind of polysaccharide found between the cells. Certain species of bacteria especially the streptococci produce hyaluronidases to dissolve the polysaccharides that bind the cells together. The dissolving action is believed to be associated in the blackening of infected wounds and to help the bacteria spread from the initial infection site towards other body parts. Clostridia species that cause gas gangrene utilize the enzyme when they infect their hosts. Like bacterial kinases, the action of hyaluronidases has promising medical application. It could be added with a drug to promote the spread of the drug in a target body tissue. (Konopka and Gedney 2003; Wilson et al. 2002)
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Clostridia species not only produce hyaluronidases but also produce collagenase (Wilson et al. 2002) that breaks down protein collagen (main component of connective tissues) into its constituent peptides and amino acids. Again, collagenase helps the spread of bacteria in infected body tissues and organs.
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The body produces a class of antibodies called IgA antibodies that inhibit the adherence of pathogenic microbes to our mucosal surfaces (Wilson et al. 2002; Lehman 2003). There are certain bacterial strains that produce IgA proteases that destroy the IgA antibodies. If they successfully wiped away the antibodies, they can now penetrate the mucosa and infection then begins. Examples of bacteria that produce IgA proteases are Neisseria gonorrhoeae and N. meningitides, the causative agents for gonorrhea and meningococcal meningitis respectively.
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Konopka A, Furbacher P, and C Gedney. 2003. Introduction to Microbiology. Pearson Education, Limited.
Lehman, Don. 2003. Introduction to Microbiology. Kendall Hunt Pub Co.
Wilson M, Mcnab R , and B Henderson. 2002. Bacterial Disease Mechanisms: An Introduction to Cellular Microbiology. Cambridge University Press.