Exam 22: Bacteria and Archaea

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a.Capsules: Many bacteria are surrounded by a capsule, which is typically composed of polysaccharides. The capsule protects the bacterium from the host animal's immune system. For example, Streptococcus pneumoniae strains that are encapsulated can cause pneumonia, while those without capsules are nonvirulent.
b.Pili: Pili are short protein appendages found in a number of bacteria. These help bacteria to bind to animal cells. Neisseria gonorrhoeae, which causes gonorrhea, has pili that allow it to attach to cells of the throat, eye, urogenital tract, or rectum in humans.
c.Exotoxins: A number of bacterial lineages produce exotoxins. These are toxic proteins that are secreted from the bacterium and interfere with the biochemical processes of body cells in various ways. For example, the botulinum exotoxin causes muscle paralysis by interfering with the transmission of nerve impulses.
d.Endotoxins: Gram-negative bacteria can cause disease through endotoxins, which are lipopolysaccharides released from the outer membrane when bacteria die and lyse. Endotoxins cause disease by overstimulating the host's immune response, often triggering inflammation.
e.
Exotoxins: Some bacteria release exotoxins, which are catalytic proteins. These may break down cell membranes (causing cells to rupture), collagen (causing connective tissue disorders), and red and white blood cells (leading to anemias and weakening of the immune system). Bacteria that release exotoxins include Streptococcus and Clostridium.