How did Robert Koch show that different microorganisms cause different infections?

Robert Koch demonstrated that specific microorganisms cause distinct infections by developing rigorous experimental techniques and establishing a set of criteria known as Koch’s postulates.

Rather than simply observing bacteria, Koch perfected pure-culture techniques, which allowed him to isolate and grow specific organisms outside the body on solid substrates. By inoculating animals with these isolated cultures, he could reproduce the original disease, thereby proving a definite causal relationship.12

His methodology included:
* Advanced Observation: He invented the hanging-drop technique and staining methods to observe, photograph, and identify specific bacteria.32
* Experimental Inoculation: In his 1878 study on wound infections, he produced six distinct types of infection by inoculating animals with specific materials, demonstrating that each was caused by a unique microorganism.2
* Systematic Criteria: He formalized four postulates requiring that a specific organism be associated with a disease, isolated in pure culture, shown to cause the disease in healthy hosts, and re-isolated from those hosts.2

These innovations provided the scientific foundation for modern bacteriology and pathology.2