Investigating antimicrobial resistance mechanisms in Neisseria gonorrhoeae using peptide probes

Abstract

The continuing evolution of antibiotic resistance strains of Neisseria gonorrhoeae coupled with the paucity of new antimicrobial agents makes the treatment of gonococcal infections challenging. A major cause of resistance is the expression of a multidrug efflux pump termed MtrCDE, which exports a wide range of antimicrobial agents. Efflux pumps are membrane-bound systems and consequently challenging to study and target with drugs. The transcriptional regulator (MtrR) of the efflux pump, however, is a soluble protein and therefore more amenable to study and drug target validation investigations. This thesis serves to investigate the hypothesis that substrates for the MtrCDE efflux pump are also ligands for the regulator MtrR. Isothermal titration calorimetry (ITC) was used to show that MtrR binds commercial antibiotics and antimicrobial peptides. -lactam antibiotics not only bind MtrR but are hydrolysed by the multidrug protein. Evidence for this novel enzymatic activity is provided by ITC, mass spectrometric and microbiological techniques. A series of peptides derived from LL-37 were synthesised and screened for binding to MtrR. A key region of LL-37 with a higher affinity to MtrR than the natural product was then identified. The peptide binding site in MtrR was elucidated via a photoactivated peptide binding study. Electrophoresis mobility shift assays indicated that the peptides do not induce derepression of the genes controlled by MtrR, although the peptide derivatives of LL-37 were shown to be substrates for the MtrCDE efflux pump