The Persian shallot has been used in Asian medicine for many generations, with a recent study suggesting that compounds from shallots could be used alongside antibiotics. The paper tested many different shallot compounds against a variety of bacterial species. Several compounds were shown to effect drug efflux – inhibiting a pump used to remove toxins from the cell. Ethidium bromide is a known substrate for the pump, which is also handily fluorescent. Monitoring the fluorescence within the cell shows whether ethidium bromide is being pumped out of the cell.
This graph plots fluorescence over time, with the orange line showing the fluorescence when the pumps are shut, and the bottom line showing the effect of a drug that doesn’t affect the efflux pumps. The four compounds in the middle all caused an increase in fluorescence, showing that ethidium bromide remains inside the cells, meaning that the pumps must have been inhibited.
So, the scientists had their first result: shallot compounds could prevent cells from removing toxins from the cell.
Efflux pumps also have a second function of kick-starting the formation of a biofilm. Biofilms are a common defence mechanism for bacteria, with cells working together to create a mesh-like structure. This is a common strategy for drug-resistant bacteria, with the cells on top of the biofilm protecting the cells below them from the worst of the antibiotics. The observations recorded showed that biofilms got thinner with increasing concentrations of shallot compounds.
Overall the scientists discovered two things: that the shallot compounds stopped the removal of toxins (and potentially antibiotics) from the cell via drug efflux, and that by doing this it prevented the formation of biofilms. Applying this knowledge to new drug development may mean that we can make more effective antibiotics that give the bacteria (including “superbug” MRSA) less chance of surviving.