Q5. You have two broth samples, one of E. coli and one of endospores from Bacillus....

Q5. You have two broth samples, one of E. coli and one of endospores from Bacillus. Both samples are placed on the surface of TSA plates with a sterile swab to obtain complete coverage on the surface of the plate. The lid of the plate is removed to expose one side of each plate to UV light for 3 minutes. The plates are incubated for 24 hours at 37^oC.

After 24 hours at 37^oC, which plate would you expect to have more growth after exposure to the UV light? Explain why?

6. In the skin flora lab you have found a very very small colony of gram positive rods (also described as diphtheroids) but the label came off the plate indicating which TSY plate (aerobic or anaerobic).

A. Which TSY pate will these cells come from, the plate incubated aerobically or the plate incubated anaerobically?(1)

B. Name the likely organism (Genus name) found on the skin. (1)

Solutions

Expert Solution

Question 5:-

The answer is Bacillus. The plate which have bacillus endospores will have more growth.

Reason :- Endospores are highly resistant to UV light exposure around 50 times more resistant than normal cells. Reason for this resistance is partly due to presence of DNA repair, in particular SP-specific repair, during spore germination. This SP repair mechanism provide protection against UV radiation and can repair the DNA before and during spore germination. Meanwhile E. coli do not have spores as they non spore forming bacteria.

Question 6:-

Part (a) :- The answer is Aerobic plate of TSY culture

Reason :- As the question state, the culture is of diptheroids and these bacteria are Aerobic in nature since they are found on the skin which is exposed to air. If they were anaerobic, they will grow in conditions which are anaerobic like in guts of human.

Part (B) Again, as the question state that they are Rods and Gram positive cells the most likely answer to this is Corynebacterium.

Corynebacterium is a genus of bacteria, also called diptheroids and they are even though ubiquitous in nature, their main reservoir is human. They can inhabit an individual's skin and are in fact the most commonly isolated bacterial genus found on human skin.

gladiator answered 1 year ago

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