Search results
Results From The WOW.Com Content Network
If the bacteria possess catalase (i.e., are catalase-positive), bubbles of oxygen are observed when a small amount of bacterial isolate is added to hydrogen peroxide. The catalase test is done by placing a drop of hydrogen peroxide on a microscope slide. An applicator stick is touched to the colony, and the tip is then smeared onto the hydrogen ...
E. coli is a gram-negative, facultative anaerobe, nonsporulating coliform bacterium. [18] Cells are typically rod-shaped, and are about 2.0 μm long and 0.25–1.0 μm in diameter, with a cell volume of 0.6–0.7 μm 3. [19] [20] [21] E. coli stains gram-negative because its cell wall is composed of a thin peptidoglycan layer and an outer membrane.
Escherichia coli is one of the most important model organisms, and its genetics and biochemistry have been closely studied. Some enterobacteria are important pathogens, e.g. Salmonella, or Shigella e.g. because they produce endotoxins. Endotoxins reside in the cell wall and are released when the cell dies and the cell wall disintegrates.
Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen. The clinically important anaerobes in decreasing frequency are: [2] 1. Six genera of Gram-negative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium, Bilophila and Sutterella spp.); 2.
Aerobic organisms produce superoxide dismutase and catalase to detoxify these products, but obligate anaerobes produce these enzymes in very small quantities, or not at all. [1] [2] [3] [5] The variability in oxygen tolerance of obligate anaerobes (<0.5 to 8% O 2) is thought to reflect the quantity of superoxide dismutase and catalase being ...
The adjectives gram-positive and gram-negative derive from the surname of Hans Christian Gram, a Danish bacteriologist; as eponymous adjectives, their initial letter can be either capital G or lower-case g, depending on which style guide (e.g., that of the CDC), if any, governs the document being written. [25]
Escherichia coli have an incubation period of 12–72 hours with the optimal growth temperature being 37 °C. Unlike the general coliform group, E. coli are almost exclusively of fecal origin and their presence is thus an effective confirmation of fecal contamination. Most strains of E. coli are harmless, but some can cause serious illness in ...
While many Escherichia are commensal members of the gut microbiota, certain strains of some species, most notably the pathogenic serotypes of E. coli, are human pathogens, [7] and are the most common cause of urinary tract infections, [8] significant sources of gastrointestinal disease, ranging from simple diarrhea to dysentery-like conditions, [3] as well as a wide range of other pathogenic ...