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Unformatted text preview: 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