One strategy for enhancing the effect of natural marine antifouling compounds has been to combine them with coumarin-type molecules (VL2, VL17 and VL19). These molecules are known to have an inhibitory effect on the efflux pumps (EP) of a large number of Gram-negative bacteria. To this end, they have been used as adjuvants to natural marine compounds (OB1, AS194 and AS162) to enhance their antibiofilm activity. On the other hand, the combination of synthetic analogues with coumarins had a synergistic effect on adhesion and biofilm formation in the bacterial strain studied, Pseudoalteromonas ulvae. In this strain, coumarins increased the effect of AS194 on adhesion and biofilm. This increase was more marked with the coumarins VL17 and VL19. These results were confirmed by EC50 calculations. With regard to adhesion, the EC50 of OB1 alone showed a reduction in combination, from 31.7 to 65.3%. As for AS194 and AS162, reductions ranged respectively from 16.9 to 43.6% and from 11.6 to 30.2%. With regard to biofilm, these two compounds in combination showed a significant decrease in their baseline EC50 in P. ulvae TC14. This EC50 decrease was marked by reduction rates ranging from 69.2 to 75.3% for OB1 and from 65.4 to 77% for AS194. In both cases (adhesion or biofilm), the effect variation in AS162 remained relatively small. Similar results were observed with two other marine strains, namely Pseudoalteromonas lypolitica TC8 and Paracoccus spp. 4M6. This study shows that inhibition of efflux pumps by coumarins enhances the anti-biofilm effect of natural marine compounds.
Key words: Biofouling, biofilm, coumarin, efflux pumps.
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