After searching through countless web pages, and contemplating over several different microbes to write about, I decided to sacrifice the infamous "Stumping of the Chump," and go for a better known microbe. I did this because of the impact this organism had on my life. I was born in Iraq, and immigrated to the United States when I was only five months old. No one really knows how it happened; my parents say it may have been because of the extreme climate change going from a warm, arid climate in Iraq to a cold, humid climate of Minneapolis, MN, but I came down with Pertussis, otherwise known as whooping cough. Most infants receive the well-known DTP (diphtheria, tetanus, and pertussis) vaccine, followed by several "booster" shots throughout the course of their childhood. Unfortunately, my first few months of life were in a war-ridden country that didn’t have time to think about vaccinating their infants, so I had no protection against it. Well, I eventually beat it, but it didn’t go down without a fight, almost wiping me out. It also caused several weeks of hell for my parents.
Well, enough said about myself, Bordetella pertussis, the agent of pertussis, is a very small Gram-negative coccobacillus that appears singly or in pairs. It lives off of a strict aerobic metabolism, and is very fastidious. It is usually cultivated on a rich blood media, although even under these conditions, it still takes 3-6 days to form pinpoint colonies. B. pertussis colonizes the cilia of mammalian respiratory epithelium, and although it is not known to invade the tissues, recent findings have shown the bacterium in alveolar macrophages. B. pertussis promotes whooping cough in two stages, a colonization stage and a toxemic stage. The first stage causes upper respiratory ailments with fever, malaise, and coughing. The second stage begins gradually with a prolonged and paroxysmal cough that ends with the characteristic gasp, or whoop. During the second stage, B. pertussis can rarely be recovered, and antimicrobial agents have no effect on the progress of the disease.
B. pertussis produces a variety of toxins, the five most important being invasive adenylate cyclase, lethal toxin (dermonecrotic toxin), tracheal cytotoxin, pertussis toxin (PTx). The invasive adenlyate cyclase is a localized toxin, which reduces phagocytic activity and helps the organism initiate infection. It also has a hemolytic activity, causing hemolytic zones around colonies growing on a blood agar. Strangely, the adenylate cyclase toxin is active only in the presence of calmodulin, which up-regulates the activity of adenylate cyclase. The lethal toxin causes inflammation and local necrosis to nearby cells. The tracheal cytotoxin, a peptidoglycan fragment, kills ciliated cells of the trachea, and stimulates the release of cytokine IL-1, which causes fever. The PTx helps in adhesion with the assistance of another factor, filamentous hemagglutinin. It also acts to inhibit adenlyate cyclase, and so subsequently, the conversion of ATP to cAMP cannot be stopped and intracellular cAMP reach dangerous levels. This disrupts all sorts of cellular functions, and in the case of phagocytes, it decreases their phagocytic activities, such as chemotaxis, engulfment, oxidative burst, and bacteridicidal killing.
Lastly, its LPS is very unusual. It is heterogeneous, with two major forms existing, Lipid A and X, that differ in their phosphate content. The functional difference in these two forms is not well known, except that Lipid X is pyrogenic and its O-side chain has a powerful immuno-supplementing activity.
References:
http://www.bact.wisc.edu/Bact330/lecturebpertussis, Kenneth Todar, UW-Madison, 1997.
"Pathogenic Bacteriology," Dr. Glenn Songer (Web page was obtained through askjeeves.com, and so exact URL could not be obtained).
Colonization of tracheal epithelial cells by B. pertussis Gram Stain of B. pertussis
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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