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Unformatted text preview: 1 Name _______________________________________ PID_______________________ BICD100 Final Exam 3/20/06 A (1) Hospitals often experience problems with bacteria that acquire resistance to multiple antibiotics, which cause infections that are very difficult to treat. You are a microbiologist in a hospital experiencing an outbreak of infections caused by a multiply antibiotic resistant strain of E. coli. You isolate the strain and find that it is resistant to streptomycin ( str R ), ( tet R ), ampicillin ( amp R ), and kanamycin ( kan R ), but is sensitive to a less widely used antibiotic called nalidixic acid ( nal S ). Your task is to find out more about the genetic basis of antibiotic resistance in this strain to help develop a strategy for combating it. Experiment I: You transform the multiply antibiotic resistant E. coli strain with an F plasmid and are successful in isolating an Hfr version of the strain, which is str R , tet R , amp R , kan R , nal S . This strain is mated with a tamer E. coli strain that is F- and nal R , but str S , tet S , amp S , kan S . The two strains are mated; mating pairs disrupted at 5 minute intervals and plated on media containing nalidixic acid plus one other antibiotic. The following results are obtained: # of colonies growing on plates containing the following antibiotics time (per 100 Hfr cells plated): nal + kan nal + amp nal + tet nal + strep 5 min. 10 min. 15 min. 20 min. 5 6 25 min. 29 35 3 30 min. 60 61 25 35 min. 63 64 48 40 min. 64 65 52 45 min. 65 66 54 (data were collected every 5 minutes for another hour, but the results were never significantly different from the result at 45 minutes) a. On a “time of transfer map” of the multiply antibiotic resistant strain’s chromosome, how many minutes would there be between the Hfr origin of transfer and the strep r gene? (5 pts) b. How could you explain why tet R nal R colonies never appear? (5 points) Experiment II. You mate the Hfr str R , tet R , amp R , kan R nal S donor strain with the F- nal R , str S , tet S , amp S , kan S recipient strain again. After 45 minutes, the mating pairs are disrupted and plated on media containing nalidixic acid and streptinomycin. 500 colonies that grew on these plates were then tested for their ability to grow on plates containing ampicillin (amp) or kanamycin (kan), with the following results: 388 colonies grew on both amp plates and kan plates 91 colonies grew on neither amp plates nor on kan plates 19 colonies grew on kan plates but not on amp plates 2 colonies grew on amp plates but not on kan plates See next page for question c… 2 c. Use the results of experiments I and II (given on the previous page) to draw a map of the E. coli chromosome in the multiply antibiotic resistant strain showing the locations of the F insertion (put this at “zero minutes”) and the str R , tet R , amp R , kan R and nal S genes. Show the orientation of the F insertiongenes....
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This test prep was uploaded on 04/07/2008 for the course BICD 100 taught by Professor Nehring during the Winter '08 term at UCSD.
- Winter '08