Antimicrobial Activity of the Green Tea Polyphenol (-)-Epigallocatechin-3-Gallate (EGCG) against Clinical Isolates of Multidrug-Resistant Vibrio cholerae

The spread of multidrug-resistant (MDR) necessitates the development of novel prevention and treatment strategies. This study aims to evaluate the in vitro antibacterial activity of green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) against MDR . First, MIC and MBC values were evaluated by broth microdilution techniques against 45 strains. The checkerboard assay was then used to determine the synergistic effect of EGCG and tetracycline. The pharmaceutical mode of action of EGCG was clarified by time-killing kinetics and membrane disruption assay. Our results revealed that all of the 45 clinical isolates were susceptible to EGCG, with MIC and MBC values in the range of 62.5-250 µg/mL and 125-500 µg/mL, respectively. Furthermore, the combination of EGCG and tetracycline was greater than either treatment alone, with a fractional inhibitory concentration index (FICI) of 0.009 and 0.018 in the O1 and O139 representative serotypes, respectively. Time-killing kinetics analysis suggested that EGCG had bactericidal activity for MDR after exposure to at least 62.5 µg/mL EGCG within 1 h. The mode of action of EGCG might be associated with membrane disrupting permeability, as confirmed by scanning electron microscopy. This is the first indication that EGCG is a viable anti-MDR treatment.