Pure Cultures Lab Essay

Published: 2019-12-05 15:43:02
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Category: Culture

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Introduction : Pure cultures are made of only one type of organisms and can be used to study their properties. A method used to isolate pure cultures is making a steak-plate, which is a dilution process in which culture is spread over an agar plate in a certain manner. Using a loop rod, culture was taken from the tube and dragged across area 1 several time,of the agar. The agar was then turned 90º, and the loop was flamed and cooled. Taking some culture from area 1, it was dragged over area two,and the same steps were done for areas 3 and 4.Another technique used was spread-plate, where the same culture is spread over the agar plate using a sterile L-shaped bent glass rod.

The rod was dipped in 95% ethyl alcohol and flamed to sterlize. The nutrient agar was then placed on the plate, and spread with rod. An environmental plate was used to test the cultures of a random object, in our experiment, it was the ocular lens of a microscope. A cotton swab was dipped into sterile water, and a random item of our choice was swabbed. After mixing the swab back in the water, the contaminated water was applied to a spread plate.

Results: See attached

Discussion: All the plates were successful is isolating the pure cultures except the environmental. The reason for this may have been that there was no bacteria, due to the fact they had been recently cleaned. The slant agars were able to pick up on the bacteria to show the growth. The vial that had bright yellow bacteria growing was M.leuteus, showing the successful isolation and identification. Other vials that had M.Letues and S.marcescenes had a very slight shade of bacteria growth.


1. No because a when a broth culture is used, it has not been inoculated from a pure culture, the only way would be to use a streaking method or spread plate. A mix culture slant is hard to isolate, because bacteria is clumped together, getting a single colony is difficult. These may cause contamination to the bacteria during the inoculation period.

2. If there was more culture in quadrant 4 than 3, it is due to the loop being dragged back into quadrant 1. The nutrient agar that was in 1 came back to 4, and showed more culture.

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