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Koch's postulates provide a foundational framework for establishing the causative relationship between pathogens and diseases. The four postulates state that the suspected pathogen should be present in diseased animals but absent in healthy ones. It must be grown in pure culture and cause disease when introduced to a healthy host. Finally, the isolated organism must be reidentified as the original pathogen. This guide summarizes suitable tools and methods, including microscopy and laboratory culture techniques, essential for studying host-parasite interactions and verifying pathogen roles.
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KOCH’S POSTULATES Diseased animal Healthy animal The Postulates: Tools: 1. The suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals. Microscopy, staining Red blood cell Observe blood/tissue under the microscope Red blood cell Suspected pathogen Fig. 1-15 2. The suspected organism should be grown in pure culture. Laboratory culture Streak agar plate with sample from either diseased or healthy animal No organisms present Colonies of suspected pathogen Inoculate healthy animal with cells of suspected pathogen 3. Cells from a pure culture of the suspected organism should cause disease in a healthy animal. Experimental animal Diseased animal Remove blood or tissue sample and observe by microscopy Pure culture (must be same organism as before) Suspected pathogen 4. The organism should be reisolated and shown to be the same as the original. Laboratory reisolation Laboratory culture
