UC San Diego

After the golden era of antibiotic discovery, we have been falling behind in stocking up our arsenal to fight against bacterial pathogens. If this trend continues, we will eventually return to the pre-antibiotic era and millions of lives will be at risk. An alarming increase in the rate of multidrug resistant pathogens and the lack of new antibiotics are a nightmare combination that we have to conquer in order to alleviate the current dire situation and regain control over pathogens. In order to do so, in previous years scientists developed many advanced tools to search for new antibiotics. However, there is no simple way to rapidly determine the mechanism of action (MOA) of antibiotics, information which is necessary to push an antibiotic through the discovery pipeline. Here, I will present evidence to show that bacterial cytological profiling (BCP) can be used as a powerful tool in MOA studies of antibacterial molecules. BCP provides high resolution by being able to distinguish between different subgroups of compounds based on their specific activity. I also demonstrate that BCP is able to identify the MOA of an unknown compound, spirohexenolide A, as a membrane active compound that rapidly depletes the proton motive force of the bacterial membrane. Apart from BCP, I also explore additional uses of fluorescence microscopy in antibiotic studies. Fluorescently labeled antibiotics can be applied to bacterial resistance studies to provide a additional evidence about the in vitro resistance mechanism. Finally, BCP is used to gain insight into MOA of an existing antibiotic, polymyxin B. BCP and other cell biology data suggest that, at clinically relevant concentrations, polymyxin B acts upon LPS production. BCP provides a one step assay that can be applied in antibiotic discovery, eliminating a key bottleneck of the antibiotic discovery pipeline in how to rapidly determine the MOA of antibacterial molecules. BCP will promptly fill up our arsenal and provide us tools to prevent us from going back to the pre-antibiotic era