Antimicrobial activity of the green tea polyphenol (−)-epigallocatechin-3-gallate (EGCG) against clinical isolates of Stenotrophomonas maltophilia

Abstract 

Stenotrophomonas maltophilia is increasingly recognised as an important nosocomial pathogen. Treatment options are limited due to intrinsic resistance to many antibiotics as well as concerns over toxicity of the mainstay of treatment, co-trimoxazole. Epigallocatechin-3-gallate (EGCG), the major catechin found in green tea, has been shown to have antimicrobial effects against a number of bacterial pathogens. We evaluated the in vitro activity of this compound against 40 clinical isolates of S. maltophilia. MIC_50/90 values (minimal inhibitory concentrations for 50% and 90% of the organisms, respectively) were 256mg/L when determined by agar dilution and 512mg/L by broth microdilution. MBC_50/90 values (minimal bactericidal concentrations for 50% and 90% of the organisms, respectively) were 512mg/L. In time–kill assays, the bactericidal activity of EGCG was analysed by viable colony counts as well as a colorimetric assay for bacterial reduction of XTT. EGCG was slowly bactericidal at 4× MIC, with a 2.5log reduction in viable bacteria at 24h. EGCG has promising in vitro antimicrobial activity against S. maltophilia. Although the mechanism of action is not yet clear, further studies to evaluate its clinical potential and role in combination with other antimicrobial agents are warranted.

Keywords: Stenotrophomonas maltophilia, EGCG