At sufficient concentrations,
antibiotics effectively eradicate many
bacterial infections. However, during
therapy, bacteria are unavoidably exposed to lower
antibiotic concentrations, and sub-MIC exposure can result in a wide variety of other effects, including the induction of virulence, which can complicate
therapy, or horizontal gene transfer (HGT), which can accelerate the spread of resistance genes. Bacterial
type I signal peptidase (
SPase) is an essential
protein that acts at the final step of the general secretory pathway. This pathway is required for the secretion of many
proteins, including many required for virulence, and the arylomycins are a class of natural product
antibiotics that target
SPase. Here, we investigated the consequences of exposing Escherichia coli cultures to sub-MIC levels of an arylomycin. Using multidimensional
protein identification technology mass spectrometry, we found that arylomycin treatment inhibits the proper extracytoplasmic localization of many
proteins, both those that appear to be
SPase substrates and several that do not. The identified
proteins are involved in a broad range of extracytoplasmic processes and include a number of
virulence factors. The effects of arylomycin on several processes required for virulence were then individually examined, and we found that, at even sub-MIC levels, the arylomycins potently inhibit flagellation, motility, biofilm formation, and the dissemination of antibiotic resistance via HGT. Thus, we conclude that the arylomycins represent promising novel
therapeutics with the potential to eradicate
infections while simultaneously reducing virulence and the dissemination of resistance.