Fulvic acid as the active ingredient is used in the treatment or inhibition of multi-drug resistant bacteria, in particular NDM-1 bacteria producing carbapenemase or extended-spectrum &bgr-lactamase (ES8L) resistant bacteria. The multi-drug resistant bacteria may be gram negative bacteria including, but not limited to, Klebsiella pneumoniae or Escherichia coli. The fulvic acid can be provided in combination with one or more antibiotics from the class of carbapenems or polymyxin antibiotics.