The invention relates to a therapy of an infection with a drug resistant
bacterium wherein a characteristic of multivalent phenol derivatives
and/or extracts from "Tara" which enhance the activity of .beta.-lactam
antibiotics on the drug resistant bacteria is utilized. Specifically, the
invention relates to an enhancer of .beta.-lactam antibiotics comprising
a multivalent phenol derivative or its pharmaceutically acceptable salt,
a pharmaceutical composition comprising a .beta.-lactam antibiotic and a
multivalent phenol derivative and/or extract from "Tara" for the therapy
of an infection with a drug resistant bacterium, a disinfectant for the
same, and a functional food comprising a multivalent phenol derivative
and/or extract from "Tara".