Controlling Bacterial Persister Cells and Biofilms by Synthetic Brominated Furanones

Bacteria are well known to obtain tolerance to antibiotics by forming multicellular structures, known as biofilms, and by entering dormancy and forming persister cells. Both mechanisms allow bacteria to tolerate antibiotics at concentrations hundreds to thousands of times higher than the lethal dose for regular planktonic cells of the same genotype. Persister formation increases in biofilms; thus, effective control of persister cells, especially those in biofilms is critically important to infection control. Over the past decades, a bacterial signaling system based on cell density, named quorum sensing (QS), has been found to regulate biofilm formation and, in Pseudomonas aeruginosa, the level of persistence. In this study, we characterized the effects of synthetic brominated furanones, a group of QS inhibitors, on the persistence of P. aeruginosa and Escherichia coli. Our results revealed that (Z)-4-bromo-5-(bromomethylene)-3-methylfuran-2(5H)-one (BF8) can reduce persister formation in P. aeruginosa PAO1 and E. coli RP437 and restore the antibiotic susceptibility of isolated persister cells at growth non-inhibitory concentrations. In addition to planktonic persister cells, BF8 was also found to reduce persister formation in the biofilms of P. aeruginosa PAO1 and E. coli RP437. Study at the genetic level using DNA microarrays demonstrated that BF8 induced the gene mdaB in both strains and 7 genes encoding oxidoreductases in P. aeruginosa. In E. coli RP437 persister cells, BF8 was also found to repress the genes for synthesizing indole, a signaling molecule reported to induce persister formation in E. coli. Interestingly, although BF8 is a QS inhibitor, the QS signal 3-oxo-C12- acyl homoserine-lactone also rendered the persister cells of P. aeruginosa PAO1 and its mucoid mutant PDO300 more sensitive to antibiotics. Furthermore, BF8 was found to have cidal effects on PDO300. Besides BF8, some other BFs were also found to restore the susceptibility of P. aeruginosa PAO1 persister cells to ciprofloxacin. Collectively, these results indicate that this group of QS inhibitors has promising activities to control multidrug tolerant persister cells; and there might be other bacterial targets of BFs in addition to QS inhibition