Bacteria are potentially pathogenic when:
• Displaced from normal environments in the body - intestinal E. Coli transfer from rectal area into the urinary tractto cause a UTI
• Multiply out of control in an area of the body
• Not part of body's natural flora and enter body from external source - E.g. Yersinia pestis (responsible for the "Black Plague"in 14th century Europe
Bacteria may produce toxins
- Molecules in a cell wall (called adhesins) bind bacteria to the cell - once attached, the bacteria may produce poisonous substances:
• Endotoxins - parts of the cell walls of gram-negative bacteria that are toxic even after the death of the cell. Endotoxins stimulate production of cytokines that can produce widespread vasodilation and shock, and can even cause death
• Exotoxins - enzymes released by bacteria into their host, include hemolysins, leukocidins, coagulases, and fibrinolysins. Exotoxins can also be released in cell lysis (cell death), similarly to endotoxins. These toxins can destroy cells or disrupt normal cellular metabolism. E.g. Clostridium botulinum releases the neurotoxin Botox, that causes botulism. Some toxins are so potent that they can be fatal, since they do not give the immune system time to launch a defense
