MICROBIOLOGICAL SEMINARS th SEMINAR 1 (15 APRIL) 1. ln an early experiment testing the hypothesis of spontaneous generation, Francesco Redi placed raw meat in beakers, covered some of the beakers with a fine cloth, and left the remaining beakers open. Maggots appeared in the open beakers but not the covered beakers. However, the meat in the covered beakers eventually did spoil. Suggest three possible sources of the organisms that spoiled the meat. Given current day knowledge, suggest three procedures to help prevent spoilage that Redi could have incorporated as part of his experiment (only procedures that could have been done in 1688) a. Contamination of beakers, organisms on hands, meat, cloth or in air b. Salting, heating the beaker (sterilization), and boiling the jar with the meat in it (like jam). 2. Mad cow disease recently affected British cattle, nearly destroyed the British beef industry, and is still a major concern. Analysis of the dead cattle revealed tissue degradation in the brain (accounting for the erratic behaviour of diseased animals), but no foreign prokaryotic or noncow eukaryotic DNA or RNA was ever detected in cattle with mad cow disease. Recently, the world famous microbiologist Dr. Noital proclaimed that mad cow disease obeys Kochs postulates. Is Dr. Noital correct? Why or why not? a. Incorrect. Lack of nucleic aid indicated no organisms is present. Therefore cannot be isolated, grown in pure culture, infected into healthy host and recovered unchanged. (kohs postulates) 3. Despite the fact that there are many more people inhabiting the planet now than 500 to 1,000 years ago, there are many fewer epidemics today involving diseasecausing bacteria. Suggest at least three reasons for the higher incidence of disease in the past. a. Lack of hygiene, antibiotics, education, vaccines medicine, living conditions. 4. Dr. Noital performs the following experiment to determine whether a special quality of air allows spontaneous generation to occur. 1. Boiled beef broth is placed in two sterile flasks, flask A and flask B. 2. Untreated air is circulated through flask A. 3. Air treated with gamma radiation (dose sufficient to kill bacteria) is circulated through Flask B. 4. Both flasks are incubated at room temperature. l Growth of organisms occurs in flask A but not flask B. Dr. Noital reasons that organisms in the air contaminated the broth in flask A. He also reasons that the gamma radiation treatment killed the organisms in the air circulated in flask B. He concludes that growth of organisms was due to contamination, not spontaneous generation. He also concludes that there is no special quality of air that allows spontaneous generation to occur. Are Dr. Noitals reasoning and conclusions correct? Why or why not? a. Incorrect. Could be argued that treatment with gamma radiation altered some quality of air necessary for spontaneous generation. Needs control where is filtered but otherwise untreated before going through the flask. 5. If most bacteria have a diameter of 0.5 to 1.0 m, what would this range be in nanometers? In Angstroms? a. 500100nm 500010000ang 6. An average bacterium is 2.5 m in length. The human eye cannot see an object smaller than 0.1 mm. How much larger than the average bacterium is the smallest object that the human eye can see? a. 0.1mm=100um therefore 40x greater than 2.5um 7. How could you obtain 2,000x magnification with a 100x objective? Would it be worthwhile to upgrade the microscope from 1,000x to 2,000x at a considerable cost? (Hint: the smallest bacterium that it is usually useful to see is 0.5 to 1.0 m thick). a. Ocular x objective = magnification. Use 20x optical lens. Missing something unable to resolve with 2000x magnification, also not necessary since can use 1000x magnification to see most bacteria. 0.5um x 10000= 0.5 mm, 5x larger than smallest object eye can see unaided. 8. Why do you think that the refractive index of air is less than the refractive index of glass, i.e., what property of air and glass might be responsible for refractive index? a. Change of speed (refraction) is due to interaction of polarisable electrons in molecules in glass. Higher atomic density of glass responsible for difference.