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Clostridioides difficile (syn. Clostridium difficile) is a bacterium known for causing serious diarrheal infections, and may also cause colon cancer. [4] [5] It is known also as C. difficile, or C. diff (/ s iː d ɪ f /), and is a Gram-positive species of spore-forming bacteria. [6]
Bezlotoxumab is a human monoclonal antibody designed for the prevention of recurrence of Clostridium difficile infections. By x-ray crystallized structure of N-terminal of TcdB, the toxin is identified to consist of three domains: a glucosyltransferase domain (GTD), a cysteine protease and a combined repetitive oligopeptide (CROP) domain.
The most well-characterized are enterotoxin (Clostridium difficile toxin A) and cytotoxin (Clostridium difficile toxin B), both of which may produce diarrhea and inflammation in infected people, although their relative contributions have been debated. [20] Toxins A and B are glucosyltransferases that target and inactivate the Rho family of GTPases.
The toxins function by damaging the intestinal mucosa and cause the symptoms of C. difficile infection, including pseudomembranous colitis. TcdA is one of the largest bacterial toxins known. With a molecular mass of 308 kDa, it is usually described as a potent enterotoxin , [ 3 ] but it also has some activity as a cytotoxin . [ 4 ]
The concept of natural selection originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, science had yet to develop modern theories of genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical genetics formed the modern synthesis of the mid-20th century .
The Genetical Theory of Natural Selection is a book by Ronald Fisher which combines Mendelian genetics with Charles Darwin's theory of natural selection, [1] with Fisher being the first to argue that "Mendelism therefore validates Darwinism" [2] and stating with regard to mutations that "The vast majority of large mutations are deleterious; small mutations are both far more frequent and more ...
Two useful introductions to the fundamental theory underlying the unit of selection issue and debate, which also present examples of multi-level selection from the entire range of the biological hierarchy (typically with entities at level N-1 competing for increased representation, i.e., higher frequency, at the immediately higher level N, e.g., organisms in populations or cell lineages in ...
Mathematical modeling suggests that under certain circumstances, natural selection favours the evolution of canalization that is designed to fail under extreme conditions. [21] [22] If the result of such a failure is favoured by natural selection, genetic assimilation occurs. In the 1960s, Waddington and his colleague the animal geneticist J. M ...