How Bacteria Cause Disease

Since so many microorganisms exist that are not implicated in infections, how can microbes be linked with specific infections?

• Robert Koch (1834-1910) set out the criteria used to decide if a microorganism caused a disease in what are now known as "Koch's Postulates".

• These state:

  that the causative organism must be isolated from every individual suffering from the disease in question;

  the causative organism must be cultivated artificially in pure culture;

  when the causative organism is inoculated from pure culture, the typical symptoms of the infection must result;

  the causative organism must be recoverable from individuals who are infected experimentally.

These days, one would also look for antibodies to be raised against the causative organism in natural cases and in individuals infected experimentally.