Pure Culture Techniques (continued 4. What advantage(s) does the streak plate me

Question

Pure Culture Techniques (continued 4. What advantage(s) does the streak plate method have over the pour plate metho 5. What advantage(s) does the pour plate method have over the streak plate method? 6. Why is the lo flamed before it is placed in a culture tube? Why is it flamed after completing the inoculation? ore inoculating and pouring molten nutrient agar into a plate, why must the agar first be cooled to 50°C? 7. Bef o a pblin Describe the difference between the appearance of surface and subsurface colonies in a pour plate. If this is the same bacterial species, why do these differences in colonial growth occur? 9. 91

Explanation / Answer

1. Advantage of streak plate method over the pour plate method would be that there is proper isolation of the bacteria present in the mixed culture, this helps in isolation of the bacteria in pure culture. There us minimal concentration present at the end of the plate.

2. The pour plate method allows for confident growth of bacteria, which is not possible in the streak plate method, in the streak plate method there us isolation of bacterial colonies which is not possible in this case. Counting of bacteria is done more precisely in the pour plate method.

3. The loop is flamed till it becomes red hot so that there would be destruction of any microbe that might be present on the surface of the loop. This helps in avoiding any sort of contamination while streaking the plate and maintains sterile conditions. It is flamed after completion of inoculation, since any bacteria that have been streaked on to the plate would not remain on the loop. It would be destroyed to avoid any further contamination.

4. The agar, when in the autoclave, would be at 121degC. If the agar would be inoculated at this temperature using my if the culture, the heat would destroy the the bacterial cells. At this temperature, only the Bacillus stearothermophilus could survive as they are heat sensitive. If the agar is not lowered to this temperature, most of the heat sensitive bacteria would be dead, thus not giving rise to any cultures and killing most of the cultures.

5. If plates are not inverted during incubation, there would be perspiration on the top glass side of the agar plate. This perspiration would drop onto the plate, resulting in addition of water to the already fixed dilution, further diluting the cultures.

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