Question

1. in the appropriate space in table 1 below, record the results you expect to obtain after incubation. use (+) for bacterial growth (i.e., resistance to the antibiotic) and (-) for lack of growth (i.e., sensitivity to the antibiotic). in the space below the table, explain your reasoning.

table 1. growth of e. coli strains i and ii on plates used to confirm the strains resistance or sensitivity to streptomycin and ampicillin.

lab day 2. observing confirmation plates and preparing \mating\ plates

materials

for each group:
3 sterile inoculating loops
lb plate
permanent marker
plates from lab day 1
container for bacterial contaminated waste

shared between two groups:
e. coli strain i liquid culture
e. coli strain ii liquid culture

shared (optional):
37°c incubator

procedure

1. examine the confirmation plates prepared during lab day 1 and record the observed results in table 1.
2. compare the expected results and the observed results and account for any differences. compare your results to those of your classmates and account for any differences between your results and theirs.
3. using the directions below, prepare an lb agar \mating\ plate as shown in figure 3. remember that this plate is used to bring the cells of strains i and ii into close proximity so that conjugation (mating) and the transfer of dna between cells can occur. label the mating plate to identify it as belonging to your group.

a. using the same sterile technique you used during lab day 1, dip a sterile inoculating loop into the liquid culture of strain i.
b. place a drop of culture on the lb mating plate by touching the inoculated loop to the agar. remember, open the lid of the plate just enough to slip the loop under and be careful not to touch the loop to anything but the agar. do not lay the lid down on the lab bench.

Explanation:

Step1: Analyze Strain I

Strain I is resistant to streptomycin (str) as it grows on LB+str and LB+str+amp plates, and sensitive to ampicillin (amp) as it doesn't grow on LB+amp plate. On LB plate (no antibiotics), it is expected to grow as there are no inhibitory agents.

Step2: Analyze Strain II

Strain II is resistant to ampicillin as it grows on LB+amp and LB+str+amp plates, and sensitive to streptomycin as it doesn't grow on LB+str plate. On LB plate, it is expected to grow as there are no antibiotics.

Step3: Interpret Results

The expected results are based on the known antibiotic - resistance profiles of the strains. If there are differences between expected and observed results, possible reasons could include contamination, incorrect antibiotic concentration, or errors in inoculation.

Answer:

The reasoning for the expected results in Table 1 is based on the antibiotic - resistance characteristics of E. coli strains I and II. Strain I is resistant to streptomycin and strain II is resistant to ampicillin. When there are no antibiotics (LB plate), both strains are expected to grow. When the antibiotic to which a strain is sensitive is present, growth is not expected, and when the antibiotic to which a strain is resistant is present, growth is expected.