Lactobacillus acidophilus is a gram-positive bacterium commonly used in yogurt p

Question

Lactobacillus acidophilus is a gram-positive bacterium commonly used in yogurt production. It is an obligate homofermentative bacterium, which means that it is only capable of carrying out fermentation metabolism to produce lactic acid. It is also an aerotolerant anaerobe, which means it is able to tolerate atmospheric oxygen concentrations but does not use oxygen in its metabolic processes. Describe the results you would expect to obtain if you tested this bacterium using the oxidase test, nitrate reduction test, EMB agar test, and blood agar test. For each, explain the reason you would expect to observe that result.

Explanation / Answer

oxidase test

This bacterium would show the positivity for oxidase test that is because the enzyme in the presence of atmospheric O2 oxidises colourless substrate tetramethyl- p – phenylenediamine dihydrochloride to form a dark purple patch.

Nitrate reduction test

This bacterium will not show the positivity for the nitrate reduction test because as there is no formation of red/pink colour after incubation of isolates in the nitrate broth, a characteristic of Lactobacillus

EMB agar and Blood agar test

Although the growth is slightly inhibited on the EMB agar this bacterium would show the positivity for the EMB agar test. Since it is also an aerotolerant anaerobe, this bacterium would also shows the positivity for the Blood agar test.

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