
Originally Posted by
free radical
Most gram positives are obligate aerobes (Clostridia - which causes tetanus, botulism, and one or two other conditions - is an important exception.). Gram negatives can be facultative anaerobes. The clinical upshot of this is that gram positives will infect only those parts of your body that receive oxygen, whereas gram negatives can also infect portions of your body that do not receive oxygen. Virtually all bacterial intestinal disorders are caused by Gram negatives.
(BTW, mycobacteria are not intracellular pathogens. They are resistant to antibiotics because their cell wall contains a hydrophobic component that effectively seals them off from treatment.)