Disclosed herein are pharmaceutical compositions comprising a pharmaceutically effective amount of: (a) sulbactam or a pharmaceutically acceptable salt thereof, and (b) trans-7-oxo-6-(sulphooxy)-1,6-diazabicyclo-[3.2.1]-octane-2-carboxamide or a pharmaceutically acceptable salt thereof. Also disclosed is the use of these compositions in the manufacture of a medicament for the treatment of bacterial infection.