April 4, 2010 at 10:22 pm FoodMagick Argus: From Wikipedia??? ???The third postulate specifies ???should???, not ???must???, because as Koch himself proved in regard to both tuberculosis and cholera, NOT ALL ORGANISMS EXPOSED TO AN INFECTIOUS AGENT WILL ACQUIRE THE INFECTION. Noninfection may be due to such factors as general health and proper immune functioning; acquired immunity from previous ex