WHAT HAVE I LEARN?
We are doing on the Experiment 16 and Experiment 17 this week, which are the physical factors: Atmospheric Oxygen Requirements and Technique for the Cultivation of Anaerobic Microorganisms.
Microorganisms can be classified into 5 major groups according to their needs for oxygen: Aerobes, microaerophiles, obligate anaerobes, aerotolerant anaerobes and facultative anaerobes. Aerobes microorganisms require oxygen for growth, the microaerophiles only require limited amount of oxygen where excess oxygen may inhibit activities of oxidative enzyme. Obligate anaerobes require other molecules but not oxygen as their final electron acceptor. Aerotolerant anaerobes are fermentative organisms which do not use any oxygen. Facultative anaerobes can grow in either present or absence of oxygen, but they prefer growing in the presence of oxygen. By comparing the distribution of growth for each microbes that are transferred into a melted agar deep tube after incubation, we can classify the microbes into different groups. In oxygen requirement classification, Micrococcus luteus is categorized under aerobic. Bacillus cereus and Escherichia coli are group members of facultative anaerobic. For Clostridium sporogenes, they group under obligate anaerobic.
For evacuation and replacement of oxygen atmosphere in sealed jar, we used GasPak system for Experiment 17. The evolved hydrogen gas is reacted with oxygen to yield water molecules. However, we cannot get the result for this part of experiment. This is because there are oxygen that entered the system. This may be cause by too much of Petri dish is put together at the same time in the system. Clostridium sporogenes should shows growth under anaerobic condition. We also used fluid thioglycollate medium to classify the microbes. If pink colour is present, which means that there is oxydized part. All the bacterial species that is Bacillus cereus, Escherichia coli, Micrococcus luteus and Clostridium sporogenes show growth in the fluid thioglycollate.
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| Sterile brain heart infusion of C. sporogenes which shows evenly distrubution of growth through the gas producing |
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| M. luteus which produce pigmentation shows positive growth in aerobic condition |
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