Chapter 14, Problem 10P

Linezolid is a new type of antibiotic that inhibits protein synthesis in several bacterial species by binding to the

50S subunit of the ribosome and inhibiting its ability to participate in the formation of translational initiation complexes. Physicians are particularly interested in this antibiotic for treating pneumonia caused by penicillin resistant Streptococcus pneumoniae (also called pneumococci). To explore the mechanisms by which pneumococci can develop resistance to linezolid, you first want to identify linezolid-resistant strains. Next, using one of these strains as starting material, you want to identify derivatives of these mutants that are no longer tolerant of linezolid.

a.	Outline the techniques you would use to identify linezolid-resistant mutant pneumococci and linezolid-sensitive derivatives of these mutants. In each case, would your techniques involve direct selection, screening, replica plating, treating with mutagens, or testing for a visible phenotype?
b.	Suggest possible mutations that could be responsible for the two kinds of phenotypes you will identify. What types of events in the bacterial cells would be altered by the mutations? Do you think that these mutations would be loss-of-function or gain-of-function? Explain.