The thick outer matrix of peptidoglycan, teichoic acid, polysaccharides, and other proteins serve a number of purposes, including membrane transport regulation, cell expansion, and shape formation.
Almost all bacteria can be classified as gram-positive or gram-negative. The classification relies on the positive or negative results from Gram’s staining method, which uses complex purple dye and iodine. Because gram-positive bacteria have more layers of peptidoglycan in their cell walls than gram-negative, they can retain the dye.
Six common gram-positive bacteria that infect humans and their shapes follow:
Bacillus (bacilli, protective spore) - causes anthrax and gastroenteritis
Clostridium (bacilli, protective spore) - causes botulism, tetanus, gas gangrene, and pseudomembranous colitis
Corynebacterium (bacilli, no protective spore) - causes diphtheria
Listeria (bacilli, no protective spore) - causes meningitis
Note: see information on bacterial morphology.
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