Determination of the Fitness, Macrolide and Chloramphenicol Resistance of E. coli 23S Ribosomal RNA Mutants
Forster, Kevin A.
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The 238 ribosomal RNA (238 rRNA) in bacteria is the target for many classes of antibiotics, including macrolides, ketolides and chloramphenicol. Previous studies have shown that specific point mutations in the 238 rRNA gene can have a dramatic effect on macrolide resistance in bacteria, most notable of which is the adenosine at position 2058. In Deinococcus radiodurans, mutations to the A2401 site, analogous to A2058 in E. coli, bestow resistance to erythromycin, a macrolide, but do not significantly affect erythromycin binding. To determine if there is a conservation of physiology between D. radiodurans and E. coli, point mutations to the 238 rRNA of E.coli were made to mimic the 238 rRNA of D. radiodurans. While previous studies have shown that the mutations G2057A, C2611T and C2610G all confer varying levels of erythromycin resistance, by inserting the C2611 T and G2057 A mutations to mimic the D. radiodurans ring closure into E. coli, mutants were more susceptible. Additionally, it was found that the adenosine at position 2058 appears to be critical for erythromycin binding. Unlike D. radiodurans, A2058G mutants in E. coli do not bind erythromycin. The functional conservation of nucleotides between species shows high levels of conservation in the 238 rRNA gene between bacterial species. However, the difference in the mechanics of the A2058G mutation between E. coli and D. radiodurans suggests that species have unique interactions with macrolides. Future studies will be directed towards testing erythromycin binding in species that share higher conservaation of the 23S rRNA with D. radiodurans.