Purpose: To evaluate the activity of polyphenolic compounds on growth, viability, swarming motility and biofilm formation index (BFI) of pathotypes of E. coli (EPEC, EHEC and ETEC).
Methods: Minimum bactericidal concentrations (MBCs) of tannic acid (TA), gallic acid (GA), methyl gallate (MG) and epigallocatechin gallate (EGCG) were evaluated by a microdilution method. The effect of sublethal concentrations (SC) on growth and viability was assessed by the pour plate method, and cell membrane integrity by flow cytometry. Swarming motility was determined in soft LB agar. BFI was determined by a colorimetric method.
Results: The MBCs of polyphenolic compounds against three pathotypes of Escherichia coli, showed values between 80-2500 µg/ml. MG was the most effective to inhibit growth of all tested bacteria (at concentrations of 80-600 µg/ml), while TA was the less effective (1800-2400 µg/ml). EPEC was the most susceptible (80-2100 µg polyphenols/ml), while ETEC was the most resistant (600-2400 µg polyphenols/ml). SC of compounds did not affect bacterial growth. All compounds at SC reduced swarming motility by 20%-100%. TA exhibited the highest reduction of swarming motility at 1250 mg/mL (100%) for EHEC and ETEC. Most compounds reduced BFI, but at various concentrations it was induced. GA produced the greatest inhibitory effect on BFI of EHEC and ETEC. TA induced BFI of EPEC, while MG and EGCG induced BFI of EHEC and ETEC.
Significance: All polyphenols showed bactericidal activity against E. coli of three pathotypes, although SC had different effects on phenotypic traits, and various compounds increased the expression of virulence factors.