help me with these question sum1 plz

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help me with these question sum1 plz

Post by sanj123 » Tue Mar 28, 2006 2:45 pm

Can some1 plz help me with these question please

Two different isolates of E.coli, E.coli Y and E.coli Z , were found to have the following phenotypes:

E.coli Y did not require an additional supplement in order to grow on minimal medium ( i.e. prototrophic) and was sensitive to antibiotic A (Ab A).

E.coli Z was an auxotrophic mutant, requiring serine to be added to MINIMAL medium in order for growth to occur. It was also resistant to Ab A.

Equal numbers of cells from E.coli Y and E.coli Z were mixed together and grown on nutrient agar overnight. The overnight growth was suspended in 200l saline and dilutions were plated onto different types of media. The results were as follows:

MEDIUM No of colonies per plate

Minimal medium containing Ab A 100
Nutrient agar containing Ab A 7 x 107
Minimal medium 6 x 107

(All antibiotics used at 2 x M.I.C.)

1. What were the cell counts / ml on the three media?

2. Which types of cells were present in each of the 3 counts and WHY?

It was subsequently discovered that E.coli Q was resistant to antibiotic A, and also resistant to antibiotic B (Ab B) AND to antibiotic C (Ab C).
The 100 colonies obtained on minimal medium containing Ab A were screened for resistance to Ab B and Ab C. All were resistant to Ab B but all were sensitive to Ab C.

3. Give a possible explanation for the difference between Q and the 100 colonies.

4. Describe how you would efficiently (minimal experimental effort!) perform the screening of the colonies from 1ml of the minimal medium containing AbA for resistance to other antibiotics.

Discuss BRIEFLY the possible mechanisms of resistance to the three antibiotics in relation to the results above, given that:

5. Ab B is the antibiotic gentamicin
6. Ab C is rifampicin
7. Ab A is amoxycillin

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Post by Khaiy » Tue Mar 28, 2006 4:02 pm

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Post by canalon » Tue Mar 28, 2006 10:59 pm

1- simple math (I guess tha 6x107 stand for 6x10e7)
2- use your brain, it shouldn't be too complicated to figure out...
3- Well since the Q strains is not described more it is not very complicated to explain. If one is ready to use ones brain.

4- Well read the experimental design of the beginning and it shouldn't be hard to figure out how to look for reistants.

Discussion: you have to look for antibiotic resistance mechanisms to those antibiotics. They are probably in your textbook, Otherwise you could start having a look here

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

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