A.forgetting to sterilize the loop prior to obtaining the inoculum B.flaming the

Question

A.forgetting to sterilize the loop prior to obtaining the inoculum

B.flaming the loop immediately after obtaining the bacterial sample

C.forgetting to flame the loop before streaking sequential sections of the plate

D.allowing the loop to cool for too long before proceeding

E.not creating a small section of overlap across sequential sections

A. culturing bacteria that stick together or grow as chains or clusters (such as Streptococcus and Staphylococcus).

B. transferring bacteria from a petri plate (as opposed to liquid culture as shown in the video).

C. isolating colonies from a mixed culture containing different bacterial species.

D. calculating the concentration of viable cells in a culture.

Explanation / Answer

1. In the dilution streaking procedure, a colony is picked up from an agar plate containing isolated colonies and transferred to a new agar plate with a sterile nichrome loop. The loop with culture is streaked over the surface. As a result, many microorganisms are transferred to the agar surface. The loop is sterilized, cooled, and touched to the streaked area. A small amount of bacteria is picked up by the loop and streaked in another part of the far plate. Similarly, the cycles of loop sterilization, cooling, and streaking are repeated to obtain isolated colonies. This method can include the T streak and a four-quadrant streak method

Flaming the loop immediately after obtaining the bacterial sample, will kill all microorganisms in the loop. As a result, no organism will be transferred to the new agar plate, and no isolated colonies will be seen.

Forgetting to flame the loop between sequential sections of the plate, will also not give isolated colonies. This is because a large number of organisms will still be present in the loop. Flaming between subsequent streaking, ensures that smaller number of organisms are picked up at each streak steps. Hence, the organism will be transferred in smaller and smaller numbers, giving isolated colonies.

The culture from the first streak is picked up after flaming and streaked into the next quadrant with only overlap with first two streaks that overlapping the first streak. A small section of overlap with previous streak is necessary so that organism from first streak will be transferred to the next quadrants.

Forgetting to sterilize the loop before inoculation will result in contamination. Allowing to cool the loop can cause contamination if performed too far from the burner but does not affect the isolation procedure.

Right Option are B, C, and E.

2. Steak plate method can be used to separate mixed population of bacteria as it gives isolated colonies. It can be used for organism that grow in chains or clusters, as they will still form a colony. It can be used for isolating organism from plate culture. However, it is a qualitative technique. It is not used for viable counts as only a loopful of culture is used. Isolated colonies are only obtained on last quadrants of streaks. Hence, it is difficult to calculate the counts.

Right option is D.

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