![]() ![]() As discussed later in the chapter, B fragilis is capable of elaborating numerous virulence factors, which contribute to its pathogenicity and mortality in the host. coli strains are harmless, but some serotypes such as EPEC, and ETEC are pathogenic and can cause. gram-negative motile, obligate anaerobic rods and spirochetes proliferate. Escherichia coli ( / rki kola /) 1 2 is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. B fragilis group species are the most common species recovered in some series of anaerobic bacteremia, and these organisms are associated with a very high mortality rate. variety of both aerobic, and facultative and obligate anaerobic bacteria. ![]() ![]() Both B fragilis and B thetaiotaomicron are implicated in serious intrapelvic infections such as pelvic inflammatory disease and ovarian abscesses. These infections are often polymicrobial. Bacteroides species are most often implicated in intra-abdominal infections, usually under circumstances of disruption of the intestinal wall as occurs in perforations related to surgery or trauma, acute appendicitis, and diverticulitis. A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Since aerobic respiration is more efficient, facultative anaerobes will. Gram positive bacteria have a thick peptidoglycan cell wall that stains with crystal violet. Other commonly isolated members of the B fragilis group include Bacteroides ovatus, Bacteroides distasonis, Bacteroides vulgatus, and Bacteroides thetaiotaomicron. The operator can stain the bacteria using a gram stain or an acid-fast stain. Aerobic bacteria require oxygen whereas anaerobic bacteria do not. Normal stools contain 10 11 B fragilis organisms per gram (compared with 10 8/g for facultative anaerobes). Gram-Negative Facultatively Anaerobic Rods is a descriptor in the National Library of Medicines controlled vocabulary thesaurus, MeSH (Medical Subject. Often, bacteria that are facultative anaerobes are called “aerobes.”īacteroides species are normal inhabitants of the bowel and other sites. Streptococcus species and the Enterobacteriaceae (eg, Escherichia coli) are among the many facultative anaerobes that cause disease. Bacteroides and Clostridium species are examples of anaerobes.įacultative anaerobes: Bacteria that can grow either oxidatively, using oxygen as a terminal electron acceptor, or anaerobically, using fermentation reactions to obtain energy. Facultative anaerobes are bacteria that normally breathe aerobically but switch to anaerobic respiration when oxygen is scarce. A functional definition of anaerobes is that they require reduced oxygen tension for growth and fail to grow on the surface of solid medium in 10% CO 2 in ambient air. Some Bacillus species and Mycobacterium tuberculosis are obligate aerobes (ie, they must have oxygen to survive).Īnaerobic bacteria: Bacteria that do not use oxygen for growth and metabolism but obtain their energy from fermentation reactions. Aerobic bacteria: Bacteria that require oxygen as a terminal electron acceptor and will not grow under anaerobic conditions (ie, in the absence of O 2). ![]()
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