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Koch's Postulate Demonstration with Plant Pathogen

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Erika Suarez

on 23 October 2012

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Transcript of Koch's Postulate Demonstration with Plant Pathogen

Plant Pathogen Koch's Postulate Disease: Soft Rot Conclusion Cause: Erwinia 1. ASSOCIATION: The suspected pathogen must be consistently associated with the diseased plant (or animal).

2. ISOLATION: The pathogen must be isolated and grown in pure culture and its characteristics described.

3. INOCULATION: The pathogen from pure culture is inoculated into a healthy plant of the same species or variety and it must produce the same symptoms and signs.

4. RE-ISOLATION: The pathogen is re-isolated from the inoculated plant and its characteristics must be the same as the organism initially isolated in step 2. Koch's Postulates Gram Stain: Negative rod-shaped Identification of Pathogen E. carotova was the first isolated from the carrot and therefore named after it. It infects carrots as well as tomatoes, onions, potatoes, cucumbers, lettuce and ornamental plants. Decays plant tissue Watery Foul smell Soil How it's spread Aerosols Guts of insects Water E. caratova does have a subspecies that strictly infects potatoes at temperate temperatures, but infects a wider variety of hosts at warmer climates. Source: http://www.agron.iastate.edu/plantscience/Kochs_postulates.htm IMViC Indole: Negative Methyl-Red: Negative Voges-Proskauer: Negative Citrate: Positive H2S: Negative Ornithine: Positive Lysine: Negative FTM: top 2/3 cloudy therefore, facultative anaerobe After having associated a pathogen with the disease at interest, the pathogen was then isolated and purified. A healthy plant was then inoculated with the purified culture and the same symptoms were observed in the newly diseased plant as in the original diseased plant. The pathogen was then tested, characterize, and most closely identified as being Erwinia. Steps Taken First, it was determined which plant would be used: Carrot
Next, the disease of interest was determined: Soft Rot
Then, the cause of disease was researched: Erwinia A carrot was placed in warm, moist potting soil and kept at room temperature to help induce growth of the pathogen. The "disease" was observed on the skin of the plant, isolated, and incubated at room temperature. Two different colonies were observed. Both of these colonies were further purified on separate TSA slants. Next, a healthy carrot was cut up and infected on the outer skin with the colonies that had been isolated from the infected carrot. From the results of the newly infected pieces of carrot, it was determined which "pathogen" caused the disease. The "pathogen" was then classified using biochemical tests then compared to those in Bergey's Manual in order to fully identify it. Erwinia is a genus from the Enterobacteriaceae family, that is a motile gram negative rod-shaped and facultatively anaerobic bacteria that occurs in plants. Sources:
Dictionary of Food Sciences and Technology (2nd Edition) Catalase: Negative Oxidase: Positive Enterobacteriaceae Motility: Positive
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