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''Clostridium difficile'' (etymology and pronunciation), also known as ''C. difficile'', ''C. diff'' ( ), or sometimes CDF/cdf, is a species of Gram-positive spore-forming bacteria. Clostridia (members of the genus ''Clostridium'') are anaerobic, motile bacteria, ubiquitous in nature, and especially prevalent in soil. Under the microscope, they appear as long, irregular (often drumstick- or spindle-shaped) cells with a bulge at their terminal ends. Under Gram staining, ''C. difficile'' cells are Gram-positive and show optimum growth on blood agar at human body temperatures in the absence of oxygen. When stressed, the bacteria produce spores that are able to tolerate extreme conditions that the active bacteria cannot tolerate. ''C. difficile'' may become established in the human colon; it is present in 2–5% of the adult population.〔 Sometimes antibiotic therapy for various infections has the adverse effect of disrupting the normal balance of the gut flora, in which case ''C. difficile'' may opportunistically dominate, causing ''Clostridium difficile'' colitis. == Human pathogen == Pathogenic ''C. difficile'' strains produce multiple toxins. 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 patients (''Clostridium difficile'' colitis), although their relative contributions have been debated.〔 Toxins A and B are glucosyltransferases that target and inactivate the Rho family of GTPases. Toxin B (cytotoxin) induces actin depolymerization by a mechanism correlated with a decrease in the ADP-ribosylation of the low molecular mass GTP-binding Rho proteins. Another toxin, binary toxin, also has been described, but its role in disease is not fully understood. Antibiotic treatment of ''C. diff'' infections may be difficult, due both to antibiotic resistance and physiological factors of the bacteria (spore formation, protective effects of the pseudomembrane).〔 The emergence of a new, highly toxic strain of ''C. difficile'', resistant to fluoroquinolone antibiotics, such as ciprofloxacin and levofloxacin, said to be causing geographically dispersed outbreaks in North America, was reported in 2005. The U.S. Centers for Disease Control in Atlanta warned of the emergence of an epidemic strain with increased virulence, antibiotic resistance, or both. ''C. difficile'' is transmitted from person to person by the fecal-oral route. However, the organism forms heat-resistant spores that are not killed by alcohol-based hand cleansers or routine surface cleaning. Thus, these spores survive in clinical environments for long periods. Because of this, the bacteria may be cultured from almost any surface. Once spores are ingested, their acid-resistance allows them to pass through the stomach unscathed. They germinate and multiply into vegetative cells in the colon upon exposure to bile acids. A 2015 CDC study estimated that ''C. diff'' afflicted almost half a million Americans and caused 29,000 deaths in 2011. The study estimated that 40 percent of cases began in nursing homes or community health care settings, while 24 percent occurred in hospitals. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Clostridium difficile (bacteria)」の詳細全文を読む スポンサード リンク
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