Bios242 Lab2 Essay

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iLab #2

Carbohydrate Tests


For this experiment we will be testing four different bacteria with four different tests, using glucose, lactose, and sucrose. Hopefully we will use the information from those test to be able to identify the organisms in each of the samples from the case studies. We will use the results from the four different tests along with the information of how different bacteria react to match up to the case scenario and identify the bacteria, then check to see if our guess was correct. The findings are that we were able to identify, by process of elimination, the four different test bacteria.


These procedures were followed
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This microbe was identified from colonies appearing on both plates.

Gram stain results: gram negative rods.

Acid from glucose: positive.
Gas from glucose: positive.
Lactose fermentation: negative.
Sucrose fermentation: positive.


Carbohydrate testing utilizes the different ways that bacteria metabolize different sugars by inoculating different broths with the test bacteria and seeing if there is a change in acidity and/or if any gases are produced. For glucose testing, we would check to see if gas is produced and if the ph of the broth solution drops for a positive test result. For lactose, we check to see if the ph drops or becomes more acidic. For sucrose we check the same was as for lactose but use a sucrose solution instead. A negative result would mean that the solution contained a base/alkali ph.

In order for the media to show the change in acidity the solutions are modified and include an indicator chemical. This indicator will change color depending on the ph level of the media it is in. For all the media used in this experiment, the indicator changes to a yellow color when in the presence of an acid and turns magenta/pink when in the presence of a base or alkali.

Growth can still be accomplished without metabolizing the sugar in the carbohydrate test medium by other means. The

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