Fig. 2

Effects of the kefir on bacterial quorum sensing and bacterial biofilms. a Schematic description of the generic bioluminescence induction mechanism in the reporter QS Gram-negative bacterial strains. b QS inhibition in the bioluminescent reporter strains Vibrio cholerae MM920, Agrobacterium tumefaciens A136; QS activation observed in the case of Vibrio harveyi MM30. Bioluminescence recorded upon addition of the kefir crude extract in different dilutions. The respective autoinducers (CAI-1, C8-HSL, DPD) correspond to the control experiments (no inhibition/activation of bioluminescence). c Bar diagrams showing biofilm volumes percentage generated in three wild-type bacterial strains upon addition of the kefir crude extract to the growth media (striped bars) and non-treated bacteria (solid bars). The graph displays the means (±SD; n = 3) of biofilm volume per area, generated from three independent sets of confocal fluorescence microscopy experiments calculated through the IMARIS software. p value: * p < 0.12, **p < 0.01, ***p < 0.002 calculated by ANOVA followed by Tukey’s post hoc analysis. d Viability analysis of bacterial cells in the biofilms. Staphylococcus aureus, Salmonella enterica, and Pseudomonas aeruginosa viable cells were stained in green while dead cells were stained red with the BacLight® Dead/Live Kit