As opposed to gram-positive cells, gram-negative cells are resistant to lysozyme and penicillin attack. The gram-negative outer membrane which contains LPS, an endotoxin, blocks antibiotics, dyes, and detergents protecting the sensitive inner membrane and cell wall.
LPS is significant in membrane transport of gram-negative bacteria. LPS, which includes O-antigen, a core polysaccharide and a Lipid A, coats the cell surface and works to exclude large hydrophobic compounds such as bile salts and antibiotics from invading the cell. O-antigen are long hydrophilic carbohydrate chains (up to 50 sugars long) that extend out from the outer membrane while Lipid A (and fatty acids) anchors the LPS to the outer membrane.
Examples of gram-negative bacteria:
Spirochetes (spiral-shaped) - causes syphilis, lyme disease
Neisseria (cocci) - causes meningococcus, gonorrhea
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