Gram Staining Essay

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Gram staining was used to distinguish the unknown microbes between gram-positive microbes from gram-negative microbes. Gram-positive microbes contain a thick peptidoglycan with only one outer cell membrane, thus dying the microbes dark purple. Gram-negative microbes contain a thin peptidoglycan with an outer and inner cell membrane, dying the microbes pink when a gram stain test is done. Microbes A and C were gram- positive because of purple dye seen under the microscope. Microbe B was a gram-negative because of the light pink dye seen under the microscope. The gram stain tests can be seen in figure 1. The endospore stain was used to verify that microbe C contained endospores. When tested, microbe C did have endospores.
Table 4 describes selective media tests. EMB was used for lactose fermentation and growth of gram-negative bacteria . Microbe A and microbe B turned dark purple and were able to produce lactose fermentation while Microbe B was not able to turn purple but pink which was interpreted as a negative result for lactose fermentation. PEA test was used
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In table 5, it is seen that only microbe A was able to produce a biochemical reaction for the Methyl Red test, meaning that it changed to a red color and is capable for mixed acid fermentation. In the Voges-Proskauer test, it was interpreted that microbe B was able to produce a biochemical reaction because it turned a slight reddish-brownish copper meaning it was able to produce acetoin.
In all of the bacteria, they were able to use utilize catalase. Both microbe A and microbe B had a bubbling effect while microbe C was just able to form bubbles on top of the sample. Microbe C did not produce bubbling, but was still interpreted as having a positive biochemical reaction. The oxidase test is used to see if the microbe can produce cytochrome oxidase. Microbe A and B had a negative result for cytochrome oxidase

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