Antibacterial agent

A method for inhibiting bacterial infection by S. aureus, the method comprising:

• administering an epigallocatechin gallate derivative represented by the following chemical formula (1), an isomer thereof, or a salt thereof, wherein the isomer is a tautomer, a stereoisomer or an optical isomer:
• where:
• R1 to R6 are each a hydrogen atom, halogen, sodium, potassium, or an acyl group and may be identical to or different from one another,
• wherein the acyl group has the following chemical formula (2):
• —C(O)R17 (2),
• where R17 is a straight or branched, saturated or unsaturated hydrocarbon chain that includes a carbon number of 1 to 19, and may be substituted with one or more substituents, wherein the one or more substituents are independently selected from the group consisting of an alkyl group, amino group, an alkylamino group or a dialkylamino group,
• wherein
• at least one of R1 to R6 is the acyl group, where R17 of the acyl group of the at least one of R1 to R6 is an unsaturated hydrocarbon chain;
• R12 and R14 are a hydrogen atom, halogen, sodium, or potassium and may be identical to or different from one another;
• and
• R7 to R11, R13, R15, and R16 are each a hydrogen atom.