bPersister cells, which are tolerant to antimicrobials, contribute to biofilm recalcitrance to therapeutic agents. In turn, the ability to kill persister cells is believed to significantly improve efforts in eradicating biofilm-related, chronic infections. While much research has focused on elucidating the mechanism(s) by which persister cells form, little is known about the mechanism or factors that enable persister cells to revert to an active and susceptible state. Here, we demonstrate that cis-2-decenoic acid (cis-DA), a fatty acid signaling molecule, is able to change the status of Pseudomonas aeruginosa and Escherichia coli persister cells from a dormant to a metabolically active state without an increase in cell number. This cell awakening is supported by an increase of the persister cells' respiratory activity together with changes in protein abundance and increases of the transcript expression levels of several metabolic markers, including acpP, 16S rRNA, atpH, and ppx. Given that most antimicrobials target actively growing cells, we also explored the effect of cis-DA on enhancing antibiotic efficacy in killing persister cells due to their inability to keep a persister cell state. Compared to antimicrobial treatment alone, combinational treatments of persister cell subpopulations with antimicrobials and cis-DA resulted in a significantly greater decrease in cell viability. In addition, the presence of cis-DA led to a decrease in the number of persister cells isolated. We thus demonstrate the ability of a fatty acid signaling molecule to revert bacterial cells from a tolerant phenotype to a metabolically active, antimicrobial-sensitive state. P ersister cells are considered to be a subpopulation of stochastically produced, nongrowing (dormant) cells present in biofilm and planktonic bacterial cultures. Persister cells account for 10 Ϫ6 to 10 Ϫ4 of the total cell population of mid-exponential-phase cells and up to 1% of the total cell population of stationary-phase cells and biofilms, a pattern resembling that of a quorum-sensing mechanism (1-3). Tolerance to antimicrobials is one of the key characteristics of this subpopulation, as persisters escape killing by antimicrobials such as fluoroquinolones, which can kill slowgrowing bacteria but not dormant cells (4). It is therefore not surprising that persister cells are considered to play a major role in the resilience of bacterial populations and have recently been isolated from patients with candidiasis, from cystic fibrosis patients with chronic lung infections, and from Mycobacterium tuberculosis biofilms responsible for chronic tuberculosis (5-8).Several mechanisms have been described to contribute to persister cell formation. For instance, several genes involved in energy generation and cell maintenance have been shown to be downregulated in persister cells, further indicating that persisters are nongrowing, dormant cells (1). Among these genes were members of several operons involved in oxidative phosphorylation, including NADH dehydrogenase, ATP syn...