Lab Report 2

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Exercise 12, page 95

2. How did the results observed on the mannitol salt and EMB correlate to the Gram

reaction of the bacteria?


The results observed on the manitol salt and EMB correlated to the Gram reaction of

the bacteria very well. Infact, Escherichia coli and Pseudomonas aeruginosa both gram

negative, did not grow in the manitol salt agar as expected since manitol salt agar is

selective against the growth of negative organism. Whereas, Micrococcus luteus and

Staphylococcus Epidermidis which are gram negative grew in EMB, since EMB is

selective for the growth of negative microorganism.

3. Which medium is selective?


Both medias, manitol salt and EMB are selective since mannitol salt is selective for the

growth of gram positive and EMB allows the growth of gram negative microorganism.

Exercise 13, page 102

1. Which organism(s) gave a positive test for starch hydrolysis?

How can you tell?


The organism that gave positive test for starch hydrolysis is the Bacillus subtilis. This is due to its hydrolytic enzyme amylase. This was observed after the addition of iodine. There was an obvious clearing around areas of starch hydrolysis.

Exercise 14, page 110

2. If an organism metabolizes glucose aerobically, what result will occur in the fermentation tubes?


Since the organism requires oxygen, aerobics and fermentation is a test in the anerobic environment or no oxygen, there will be no change.

3. Were these media differential or selective?


The medias are differential since MRVP differentiates among family

Enterobacteriaciae based on production of acid end products from fermentation

of glucose. Citrate is differential since it differentiates members of genus Escherichia

from genera Enterobacter and Klebsiella.

Exercise 15, page 116

Critical Thinking

1. Why is agar used as a solidifying agent in culture media instead of gelatin?


Agar is used as a solidifying agent in culture media instead of gelatin because there are few microorganism if exist that can degrade agar structurally. Whereas, gelatin can be hydrolyse by bacterias. For instance, once gelatin is hydrolyze by an exoenzyme, it liquefies and does not solidify even though when cooled below 20 deg Celsius.

Exercise 17, page 128

2. Differentiate between aerobic respiration and anaerobic respiration.


Aerobic respiration is the release of energy from the glucose in the presence of Oxygen. The final electron acceptor is molecular oxygen (O2).

In anaerobic respiration, energy is produced from glucose without oxygen. The final electron acceptor is inorganic compounds other than O2.

Other Questions (Given by Professor)

1. Which bacteria or name bacteria can grow in 55 deg C?


Thermophilic bacteria grow at this temperature such as Bacillus stearothermophilus.

2. Name a bacteria that can grow at room temperature.


Mesophilic bacteria grow at this temperature such as Serratia marcescene.

3. Name a bacteria that produce red pigment?


Bacillus subtilis

4. Name bacteria that produce green pigment


Pseudomonas aeruginosa