The antibacterial activity against Escherichia coli ATCC 10798 and Staphylococcus aureus Mag 90 of normal sera from nine species of mammals was investigated by Avantage (Abbott). Human and rat sera showed the highest antibacterial activity against E. coli ATCC 10798, while all investigated sera did not exhibit, till the maximum concentration tested (20%), spontaneous antibacterial activity against S. aureus Mag 90. Heat inactivated sera (56 degrees C for 30 min) of all investigated species lost their antibacterial activity, but maintained their synergistic effect with sub-MICs of some antibacterial drugs, principally against E. coli ATCC 10798.
