Premium yeast fraction to reduce Salmonella

By what mode of action that yeast fraction could reduce the number of Salmonella ?

Salmanella is a serious infection of birds. pullorum and Gallinarum kills birds. They are vertically transmitted. Enteritidis and Typhimurium cause food poisoning in human beings. The strategy to deal with them has been to eliminate from the poultry flocks. All attempts should be made to prevention. yeast cultures, organic acids etc are not enough to deal with the above infections.