![]() 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. 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. 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. Other commonly isolated members of the B fragilis group include Bacteroides ovatus, Bacteroides distasonis, Bacteroides vulgatus, and Bacteroides thetaiotaomicron. Normal stools contain 10 11 B fragilis organisms per gram (compared with 10 8/g for facultative anaerobes). Virulence of this bacterium depends on a variety of factors. It is also described as non-spore-forming, flagella-containing, urease positive, and lactose fermenting. People who use proton pumps inhibitors or antacids are more prone to infections of the gastrointestinal tract. Assume that the cultures have comparable intrinsic growth rates. Give a likely reason for success of the gram-negative rod. Both cultures are known facultative anaerobes. Often, bacteria that are facultative anaerobes are called “aerobes.”īacteroides species are normal inhabitants of the bowel and other sites. Etiology Enterobacter is a genus of gram-negative, rod-shaped, facultatively anaerobic bacteria of the Enterobacteriaceae family. A sample is stained and reveals only gram-negative rods. ![]() Habitat edit The habitats of mesophiles can include cheese and yogurt. There are three basic shapes of mesophiles: coccus, bacillus, and spiral. Oxygen requirements for mesophiles can be aerobic or anaerobic. These organisms use glycolysis, the Krebs TCA cycle and electron transport chain with oxygen as the final electron acceptor. Mesophiles belonging to the domain Bacteria can either be gram-positive or gram-negative. Streptococcus species and the Enterobacteriaceae (eg, Escherichia coli) are among the many facultative anaerobes that cause disease. facultative aerobES MICROAEROPHILIC Require oxygen for growth. 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. ![]() ![]() 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). The aerobic and facultative anaerobic strains clustered in two major groups with the strains of the first main group being gram-negative fermentative rods. ![]()
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