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Unformatted text preview: Questions for Antibiotics Lecture
1. ß-lactam antibiotics are bacteriolytic and antibiotics that inhibit the ribosome are bateriostatic.
Based on this information, what do you predict antibiotics that inhibit folate biosynthesis to be?
2. Mechanisms of acquired resistance to synthetic antibiotics generally result from mutations
that alter the target with which the antibiotic interacts. In contrast, mechanisms of acquired
resistance to natural antibiotics generally results for acquisition of a new gene that encodes, for
instance, an efflux pump or an antibiotic degrading enzyme. Speculate as to why this difference
is observed. 3. You find that Haemophilus influenzae has an MIC of 100 µg/ml to trimethoprim; whereas,
you find Neisseria gonorrhea has an MIC of 10 ng/ml of trimethoprim. Both of these Gramnegative bacteria have the target of trimethoprim, folate biosynthesis. List two possible
mechanisms contributing to the different sensitivity of these two bacteria to trimethoprim. 4. You incubate a bacterium, B. periodus, in growth medium with ampicillin, and this bacterium
does not grow. (Note: B. periodus grows well in the growth medium with out ampicillin.) In
contrast, when you incubate P. microbius is the same growth medium, with the same
concentration of ampicillin, P. microbius grows well. When you incubate B. periodus and P.
microbius together in this growth medium with ampicillin, both B. periodus and P. microbius
grow well. Speculate (in broad not specific terms) as to what could account for the ability of B.
periodus to grow in ampicillin containing medium when grown in the presence of P. microbius? 5. L. acido is a gram-positive bacterium that is resistant to penicillin, which inhibits
peptidoglycan biosynthesis. This resistance is not due to biofilm formation, as the planktonic
cells of L. acido are resistant to penicillin. List TWO likely mechanisms by which L. acido may
be resistant to the penicillin. 6. C. resistus is resistant to the antibiotic methicillin. Methicillin resistance is coded for by the
metR gene that resides on a conjugative plasmid, pCR1. C. sentivus is sensitive to methicillin.
However, when you incubate C. resistus with C. sentivus, methicillin-resistant colonies of C.
sentivus are recovered. You hypothesize that the methicillin-resistant C. sentivus strains have
taken up the pCR1 plasmid from C. resistus and pCR1 is able to replicate in C. sentivus.
Describe ONE test you could perform to test this hypothesis. Describe results that would be
obtained if the hypothesis is correct. 7. You have found two species of Gram-negative bacteria, Species A and Species B, that are
resistant to ampicillin. You incubate cells of these two species, separately, with ampicillin.
After incubation, you harvest the cell-free culture supernatants, which should contain any
ampicillin remaining after the incubation. These supernatants are incubated with cells of E. coli,
which are sensitive to ampicillin. The E. coli cells die after incubation with culture supernatant
from Species A, but the E. coli cells live after incubation with the culture supernatants from
Species B. Given your knowledge of the mechanisms of antibiotic resistance, speculate as to
why the E. coli cells died after incubation with the supernatant from Species A but not Species
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- Summer '10