2. What is the drug resistance of strain I? Strain II? 3. Which plate shows grow

Question

2. What is the drug resistance of strain I? Strain II?
3. Which plate shows growth in the mating sector that cannot be explained by either strain alone? Assume that one antibiotic resistance gene has been transferred. What are the possible transfers?
4. On which plates do you expect your test colonies to grow? On which plates are you unsure? Are there plates on which you don’t expect growth? Why?
5. Describe the donor and recipient strains as well as any gene transfer that has occurred and indicate which observations led you to this conclusion.

Explanation / Answer

1. Some bacteria can be naturally resistant to antibiotics by posessing resistant genes either on a plasmid or in their genome itself. When bacteria contain the resistance genes in genomic DNA they tend grow very slowly in presence of antibiotic than when they posess the resistance genes on a plasmid. This is because, the replication process would be slowered in presence of an antibiotic, though the genes are resistant.

2. Strain I is susceptible to Amp, Nal, Amp/Nal, Strep/Nal and Amp/Strep. Starin II is susceptible to Strep, Strep/Nal and Amp/Strep.

3. Sector III shows growth in Amp/Strep plate cannot be explained by either strain alone and might be involved the plasmid transfer. Other possible transfers may occur in Amp/Nal, Strep/Nal and Amp/Strep combinations.

4. Test colonies would grow on LB plate without drug. On plates containing either Amp or Strep or Nal the growth is not sure. Growth cannot be expected in plates containing combination of drugs Amp/Nal, Strep/Nal and Amp/Strep. This is because the bacteria if not susceptible to one drug , they may be susceptible to the other drug.

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