Investigating the Effects of Osmolytes and Environmental pH on Bacterial Persisters

ABSTRACT Bacterial persisters are phenotypic variants that temporarily demonstrate an extraordinary tolerance towards antibiotics. Persisters have been linked to the recalcitrance of biofilm related infections; hence, a complete understanding of the physiology of persisters can lead to improvement of therapeutic strategies associated with such infections. Mechanisms pertaining to persister formation are known to be related to stress response pathways triggered from intra- or extra-cellular stress factors. Unfortunately, studies demonstrating the effects of osmolyte- and/or pH- induced stresses on bacterial persistence are largely missing. To fill this knowledge gap within the field, here we studied the effects of various osmolytes and pH conditions on Escherichia coli persistence with the use of phenotype microarrays and antibiotic tolerance assays. Although we found that a number of chemicals and pH environments, including urea, sodium nitrite and acidic pH, significantly reduced persister formation in E. coli compared to no-osmolyte/no-buffer controls, this reduction in persister levels was lessened in late-stationary-phase cultures. Our results further demonstrated a positive correlation between cell growth and persister formation, which challenges the general notion in the field that slow-growing cultures have more persister cells than fast-growing cultures.