Cause Of Spoilage In The Citrus Fruits example essay topic

Koch's Postulates Introduction Koch created four guidelines to determine the causal agents of disease in humans, animals, and plants. Koch proved that a disease-causing agent could be transferred from one organism to another and create the same illness. Isolation of pure cultures and the introduction of the disease-causing agent to a healthy organism will transmit the disease and infect the inoculated organism. Koch's four guidelines by which one must follow to transmit a disease from an infected organism to a healthy one are as followed: 1. The specific organism should be shown to be present in all cases of animals suffering from a specific disease but should not be found in healthy animals. 2.

The specific microorganism should be isolated from the diseased animal and grown in pure culture on artificial laboratory media. 3. This freshly isolated microorganism, when inoculated into a healthy laboratory animal, should cause the same disease seen in the original animal. 4.

The microorganism should be re isolated in pure culture from the experimental infection. In this exercise, Penicillium was utilized, a common, safe, mold. Certain species of Penicillium will spoil fruits, vegetables, grains, and grasses. Other species will ripen various chess es. Still, other species are used in the production of antibiotics. The species of Penicillium, italic um is provided for the lab because of its pronounced hyphae.

Penicillium italic um, along with Penicillium attack citrus fruits post-harvest. In this experiment, the effect of Penicillium italic um on two types of citrus fruits and one non-citrus fruits were tested. Materials & Methods 1. Pick several appropriate fruits. 2. Gently was fruit in cool, soapy water, using a scrub brush on the citrus fruits, then rinse thoroughly with cool running tap water.

3. Place citrus in a beaker and cover with a 10% bleach solution. Let soak for 10 minutes. 4. Rinse thoroughly with cool running tap water for 10 minutes.

5. Flame sterilize a teasing needle, cool, then pierce skin of disinfected fruit. 6. Unscrew cap on Penicillium italic um culture tube with one hand and flame the mouth of the tube.

7. Using the first three fingers of your writing hand, obtain a sterile applicator stick and remove a small sample of the fungus and smear over the puncture wound of the fruit. 8. Flame tube and recap. Discard swabs appropriately. 9.

Obtain a second sample with a sterile applicator stick and smear over an un punctured section of the fruit. 10. Flame tube and recap. 11. Maintain a control for the experiment. 12.

Make observations periodically (make note of the fungus' odor, shrinkage, discoloration or growth characteristics). 13. Make a slide of your inoculating organism. 14.

Disinfect all work surfaces. 15. Partially unseal bag to allow quick but aseptic entrance for sample collection. 16.

With sterile applicator stick collect a sample of spores (blue-green, moldy decay) from the infected fruit. 17. Streak a Potato Dextrose Agar plate and incubate at room temperature for approximately 5 days. 18. Observe growth of culture periodically with lid intact. 19.

Growth may appear as circular, a white fuzzy mass of mycelium or white specks that gradually change color, from white to blue-green. Observe with a. 20. Repeat cleaning and washing procedure as in steps 1-4 with appropriate number and type of fruits. 21. Reinoculate your fruits (hosts) as in steps 5-11.22.

Stain a sample of the organism that you have re isolated and compare with starting culture. 23. Observe and record periodically. 24.

Repeat procedures as in steps 14-19.25. Observe periodically. 26. At the end of the experiment, again stain your organism. Results Macro-Several weeks after initial inoculation, a substantial growth was evident. The fungal growth had a distinct odor of mold.

The same amount of growth was evident around the puncture-swabbed area as the un punctured-swabbed area. Two distinct colors of mold were observed. The newer growth was white, whereas older mold had matured to a blue-green color. Micro-Microscope views of the fungus appeared as sticks with budding hyphae. The blue-green mold had more hyphae than the white mold. Discussion Questions 1.

What disease and organism attacks oranges and other citrus fruits? Penicillium italic um & Penicillium. 2. What is the purpose of the scrub brush in the wash cycle? To clean antifungal substances from the fruit.

3. Discuss a scenario using a human disease and how Koch;'s postulates can be used. Recent developments in HIV research provide some of the strongest evidence for the causative role of HIV in AIDS and fulfill the classical postulates for disease causation (Koch's Postulates). Blood can be removed from a known HIV infected human, where the disease can be found. The disease can then be cultivated in a pure culture, outside of the original host.

The culture of the disease can then be introduced to a susceptible human. Introduction of the disease will cause the susceptible host to be infected. Blood can then be withdrawn from the second host where the same disease can be found and re isolated. 4. Can Koch's postulates be applied to all disease causing organisms? Why or why not?

No, for example, AIDS fails Postulates #1 & 3. Because the virus which causes AIDS (HIV) is not found in the blood of AIDS patients. When AIDS is introduced, HIV is developed. Diseases can evolve so that the same organism that infects another potential host is not the same that maintains the disease in the present host.

5. Answer question in Laboratory Review section for exercise 54-#1, 4 (but apply to this version of the exercise). A. What value do Koch's Postulates have? Koch's Postulates not only provided a logical basis for concluding that a particular microorganism is the etiologic agent of a given disease, but also opened the door for an enormous enthusiastic search for the causes of infectious diseases. B. Briefly indicate how you would disprove the possibility that toxin or virus was the cause of spoilage in the citrus fruits in this exercise. If another organism other than the mold (Penicillium italic um) was evident in macro- or microscopic inspection of the growth.