Identification, purification and elucidation of the mode of action of (novel) antimicrobial substances

Antibiotics are among the most frequently prescribed medications in current medicine, however there is an increasing resistance emerging against our current arsenal of antibiotics. Therefore, it is important that we do research into antimicrobial substances that uniquely work on essential pathways to make it difficult for bacteria to develop resistance. One such specific targets is the peptidoglycan precursor lipid II. In Gram-positive bacteria, the peptidoglycan is readily available from the outside and this structure is essential for bacteria to withstand the pressure from their interior (sacculus). One novel antimicrobial compounds we study in this manuscript is derived from an extract from the fungus Talaromyces atroroseus that seems to specifically interact with lipid II. We furthermore showed that Laspartomycin C inhibits peptidoglycan biosynthesis by sequestering the bactoprenol lipid carrier of this same essential peptidoglycan component, showing that inhibition of this pathway does not only happen at the level of lipid II. Further studies described in this dissertation focus on a unique peptide called Pep5 of which up to now the exact mode of action is unknown. The high activity towards pathogens such as MRSA in nanomolar concentrations suggest that it works via an interaction with a similar specific target and makes to mode of action of this peptide highly interesting. We studied the effects of this peptide on the energy metabolism in susceptible bacteria with a metabolomics approach and used genetic sequencing on resistant bacteria to elucidate what changes in the genetic code resulted in resistance development to be able to better understand what pathway this peptide interferes in. The exact mode of action remains unknown, however the characteristics of the mode of action of this peptide are distinctly different compared to known antibiotic and might entail a novel way of developing novel antibiotics to combat resistant bacteria.