The efficacy of tannic acid in controlling biofouling by Pseudomonas aeruginosa is dependent on nutrient conditions and bacterial density

This study investigated the effect of tannic acid (TA) on biofilm formation by Pseudomonas aeruginosa PAO1 as a model organism. Here, we report that TA enhanced biofilm formation in M9 medium at a bacterial concentration of 0.1 (OD₆₀₀) on different model surfaces such as: polystyrene microtiter plate, polypropylene tube and borosilicate glass tube. However, TA reduced biofilm formation by PAO1 in M9 and yeast nutrient broth (YNB) media at a bacterial concentration of 0.001 (OD₆₀₀). Strikingly, TA reduced biofilm formation at a bacterial concentration of 0.01 (OD₆₀₀) in YNB medium but increased biofilm formation in M9 medium. When yeast extract (10g/l) was added to the M9 medium TA reduced biofilm formation (51.0%). These trends were confirmed qualitatively and quantitatively by confocal microscopy. In the presence of yeast extract, TA exhibited 89.0% biofilm biovolume reduction compared to the untreated control. When yeast extract, tryptone and l-arginine were added to M9 medium, TA showed anti-biofilm activity at all bacterial densities tested. When tannase was added, the anti-biofilm efficacy of TA decreased. Furthermore, organic nitrogen limitation triggered TA degradation in the cultures (P<0.05), which in turn restored biofilm formation. These results suggest that bacterial density and nutritional conditions are critical to the anti-biofilm efficacy of TA against PAO1 and thus may explain differences in the literature regarding the effect of TA on biofilm formation.