Environmental conditions define theenergetics of bacterial dormancy and itsantibiotic susceptibility

Bacterial cells that stop growing but maintain viability and the capacity to regrow are termed dormant and have been shown to transiently tolerate high concentrations of antimicrobials. The proposed mechanism behind the enhanced survival capabilities of these cells is the reduced energy supply. However, not all reported results are in agreement, and the exact role of energetics remains unsolved. Because dormancy merely indicates growth arrest, which can be induced by various stimuli, we hypothesise that dormant cells may exist in a range of energetic states that depend on the environment. We first establish conditions that are capable of inducing dormancy, and subsequently measure the energy profiles they elicit in single dormant cells. Our simultaneous measurements of proton motive force (PMF), cytoplasmic pH and ATP concentrations confirm that dormant cells exhibit characteristic energetic profiles that can vary in level and dynamics, depending on the stimulus leading to growth arrest. We test whether the energetic makeup is associated with survival to antibiotics of different classes and find that, while growth arrest remains the dominant mechanism enabling survival, some correlations with cellular energetics exist. Our results pave the way to a classification of dormant states based on energy profiles, support a novel relationship between environment and drug susceptibility of dormant cells and suggest that knowledge of the conditions present at the infection site is necessary to design appropriate treatments.