It was reported that DSF signals learn more could modulate various biological functions including virulence, biofilm formation, antibiotic resistance and persistence through interspecies communication [23, 24, 37]. Additionally, DSF-family signals were also found to

play a role in inter-kingdom communication by inhibiting morphological transition of C. albicans[14, 17, 22]. The results from this study present a new role of DSF and its structurally related molecules, i.e., increasing the antibiotic susceptibility of some bacterial species (Figure 1, Table 2). Given that DSF at a final concentration of 5 μM, which appears to be a physiological relevant concentration [14, 22], could substantially increase bacterial sensitivity to antibiotics (Figure 2A), it appears plausible that DSF-family signals may have a role in shaping local microbial ecology as they could reduce the competitive advantage of some community residents by down regulation of their antibiotic or toxin tolerance. Furthermore, our results also suggest that

DSF and its structurally related molecules may be used as a LBH589 new kind of antibiotic adjuvant for the treatment of infectious diseases caused by bacterial pathogens, subjecting to further evaluation of their toxicological and pharmacological properties. DSF-family signals share a fatty acid carbon chain with variations in chain length, double-bond configuration, and side-chain [18]. Evidence is emerging that these structural features may contribute to their biological activity in intraspecies signalling and interspecies communication [14, 17, 37]. Our study showed that the synergistic activity of DSF and its structurally related molecules with antibiotics is influenced by their structural features. Each of these molecules has a distinct synergistic activity among which the disparity could be up to 128-fold (Figure 1A). As a general rule, our results showed that the unsaturated long

chain DSF related molecules have better synergistic activity with antibiotics, especially the aminoglycoside Progesterone antibiotics, than the short chain and saturated molecules. Meanwhile, the synergistic activity of DSF and related molecules may also seem to be affected by the mode of action of antibiotics as the synergistic activities of DSF and related molecules with aminoglycoside antibiotics such as gentamicin and kanamycin were much better than with other types of antibiotics (Figure 1, Table 2). It was reported that BDSF signalling system positively regulates the antibiotic resistance of B. cenocepacia[21]. The same research group also found that addition of DSF signal to P. aeruginosa could increase the bacterial antibiotic tolerance to polymyxins [23].