Treatment of E. coli Biofilm Using Galla chinensis and Adjuvant Chemicals

Overview

Bacterial biofilms are present in about 60% of human infections, with those consisting of Gram-negative bacteria exhibiting particularly high resistance to antibiotics. To treat infections involving biofilms, it is important to investigate antibiotic alternatives with low toxicity. Chinese herbal medicines such as Galla chinensis have been shown to exhibit anti-biofilm activity, but are not strong enough to combat infections on their own. The purpose of this study was to determine the efficacy of using cinnamaldehyde (CAD), which interferes with substrate attachment and c-di-GMP-regulated biofilm formation pathways, and zinc, which interferes with ATP production and the aforementioned pathways, in conjunction with G. chinensis to inhibit Escherichia coli biofilm formation and disperse preformed biofilm. To conduct this study, biofilms were cultivated in the presence of 0.16 mg/mL G. chinensis water extract (GWE) and varying concentrations of either CAD or ZnCl2 (0-10 mM), or were exposed to these treatments after cultivation. A crystal violet assay was used to quantify biofilm formation, and one-tailed t-tests were run to determine statistical significance of observed differences between treatments. The results demonstrated that GWE used in conjunction with CAD or ZnCl2 at a concentration of 10 mM was significantly more effective at inhibiting biofilm formation and dispersing preformed biofilm than GWE alone. The most effective treatments for inhibiting biofilm formation and dispersing biofilm were GWE combined with 10 mM CAD and GWE combined with 10 mM ZnCl2, respectively, with the former reducing formation to less than 10% of the control and the latter dispersing over 80% of the biofilm relative to the control. The synergistic anti-biofilm effects of using G. chinensis in conjunction with other natural treatments is promising for its future application in combating chronic infections.