Green tea extract weakens the antibacterial effect of amoxicillin in methicillin-resistant Staphylococcus aureus infected mice.

Tea (Camellia sinensis) has been known for its modulation of resistance of methicillin-resistant Staphylococcus aureus (MRSA) to beta-lactam antibiotics in vitro. This study aimed to confirm the in vitro effect of green tea extracts with beta-lactams and to determine whether green tea extracts can reduce the minimum inhibitory concentrations (MICs) of amoxicillin in MRSA-infected mice. The catechins in the test tea that account for the reduced resistance to beta-lactams were quantitatively determined by high-performance liquid chromatography. The MICs of the ampicillin, cefazolin, amoxicillin, oxacillin, tea extract alone and tea extract in combination with beta-lactams were determined. Proportions of tea extracts and amoxicillin-tea extract combinations were administered to groups of mice enterally. The in vitro experiment showed that the MICs of four beta-lactams were greatly decreased in the presence of 0.25% tea extract. However, in an in vivo experiment, amoxicillin in combination with 5% tea extract conferred a higher ED50 than that of antibiotic alone. Green tea extract, alone or in combination with amoxicillin, does not have protective benefits in MRSA-infected mice. This study concluded that tea extract weakened the antibacterial effect of amoxicillin in MRSA infected mice. Tea drinking is not recommended in combination with amoxicillin treatment. Copyright (C) 2009 John Wiley & Sons, Ltd.