Regulation of intrinsic antibiotic resistance systems in mycobacteria and identification of synergistic drug combinations to overcome intrinsic antibiotic resistance

Mycobacterium tuberculosis, the causative agent of tuberculosis, is an adept pathogen partly due to its intrinsic antibiotic resistance systems which make an infection difficult to treat with antibiotics. Parts of these intrinsic antibiotic resistance systems are regulated by the product of the gene whiB7. A yeast two-hybrid experiment suggested that WhiB7 might interact with the anti-sigma factor RsbW, indirectly implying involvement with the alternate sigma factor SigF. Co-expression of WhiB7 and RsbW in Escherichia coli followed by pull-down experiments did not support this hypothesis. In order to understand mycobacterial instrinsic antibiotic resistance, a new screening method was designed and implemented to identify pairs of compounds that inhibited mycobacteria by synergistic interactions. Mycobacterium bovis BCG(lux) cells were exposed to pairwise compound combinations and assessed for viability. A computer program was created to identify synergistic combination leads from the screen. The synergistic interactions might provide us with a greater understanding of the intrinsic antibtiotic resistance systems in mycobacteria. A sample of the leads from the screen tested further confirmed that 38% of domperidone combinations and 25% of rifampicin combinations were synergistic. The data from the screen has also identified new potential anti-mycobacterial compounds, specifically the avermectins. The avermectins, as a family, have never been reported to demonstrate antibiotic activity, but they have been used to treat people and other mammals for parasitic infections. The antibiotic activity of the avermectins was investigated in this work and found to be specific to mycobacteria. The potential of this compound family as a possible future treatment for tuberculosis therapy warrants further study.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat