Propionibakteerien ja laktobasillien quorum sensing -estoaktiivisuus

Bacteria coordinate the virulence factor production and biofilm formation by activating the mechanism of intercellular communication called quorum sensing (QS). The biofilm matrix protects bacteria against variety of stress conditions, including e.g., effects of antibiotics and disinfectants. QS inhibitors (QSI) are molecules that can inhibit the QS mechanism. QQ is a QSI inhibitor that interrupts the cell-to-cell signaling already outside of the bacterial cell. Dairy propionic acid bacteria have known antimicrobial properties but their ability to produce anti-QS compounds have not yet been studied. Previous studies have shown positive results of the anti-QS activity exerted by lactobacilli, but more research is needed to uncover mechanistic details behind their QS-inhibitory effects. The aim of this study was to investigate the anti-QS and QQ activity of propionic bacteria and lactobacilli. The used method was an in-house optimized screening method based on using wild-type and mutant strains of Chromobacterium violaceum. This bioreporter produces a QS-mediated, measurable color pigment. Here, the limit of potential QSI and QQ inhibition was set to 50 % inhibition. Viability of bioreporter was analyzed by resazurin staining. Propionibacterium freudenreichii strains demonstrated both the QSI (64–71%) and QQ (52–60%) activities against the tested C. violaceum reporters. In the case of lactobacilli, Lacticaseibacillus rhamnosus GG, Limosilactobacillus mucosae 2674, Lactobacillus acidophilus 80, Lactobacillus curvatus 453 and Lactobacillus kefiri 3070 inhibited the QS-activation of the wild-type bioreporter strain by 45 to 90 %. There was a great variability in the anti-QS screening assays involving the mutant strain, which may be explained by the possible sensitivity of the compounds to the analysis conditions used or more sensitive response of the mutant strain to the tested agents. In conclusion, the obtained results show that L. acidophilus 80 produced bactericidal compounds. L. reuteri 410 did not have any effect on the QS-indicator production in wild-type bioreporter but was able to inhibit QS-induction in the mutant reporter by 72% (QQ activity). This study showed that P. freudenreichii strains as well as certain lactobacilli have an ability to produce QSI and QQ activity against some gram-negative biofilm pathogens. Pathogens have different QS mechanisms and experiments with C. violaceum strains are only one way to screen for anti-QS compounds. Therefore, validation of the obtained findings requires complementary screening assays against other bacterial bioreporters, involving both gram-negative and gram-positive biofilm bacteria.