In vitro inhibitory effects of turmeric extracts against biofilm formation and virulence of flavobacterium oreochromis

Abstract

Flavobacterium oreochromis is an opportunistic bacteria and causative agent of columnaris disease that affects freshwater fish worldwide. To initiate infection, the bacteria are required to attach and form biofilm on the fish's skin. The bacteria cells in the biofilm then produce toxins that can degrade fish connective tissue, resulting in lesions and ulcers. This study aimed to evaluate the efficacy of turmeric (Curcuma longa L.) extract by three organic solvents (hexane, ethanol, and methanol) in biofilm inhibition and modulation of biofilm-associated genes of F. oreochromis. Turmeric extracts by three different organic solvents were tested for their ability to inhibit the growth and biofilm formations of F. oreochromis. The results showed that the hexane extract of turmeric was the most potent inhibitor of the growth and biofilm formation of F. oreochromis. To determine the effect of hexane extract of turmeric on biofilm-associate genes in F. oreochromis isolate no. 15, the qPCR method was used. To do this minimal inhibition concentration (MIC) and minimal biofilm inhibition concentration (MBIC) of this extract were determined for this bacterial isolate, and the concentration of extract that inhibited the bacterial biofilm but not the growth was used (1 µg/ml). The obtained results showed that turmeric extract strongly downregulated the expression of genes in the iron acquisition, type 9 secretion, and quorum sensing (luxR) systems in F. oreochromis isolate number 15 at all three-time points (24h, 48h, 72h) studied. In summary, turmeric extract inhibited biofilm formation of F. Oreochromis through the downregulations of genes in the iron acquisition (alcB, rhbC, sido, tonB), type 9 secretion (gldL, sprA. porV) and quorum sensing (luxR) systems.