Oligosaccharides produced by an alternansucrase enzyme catalyzed reaction of sucrose with an acceptor oligosaccharide are effective as prebiotics for controlling enteric bacterial pathogens. Populations of enteropathogenic bacteria may be substantially reduced or inhibited by treatment of an animal with a composition comprising one or more of these oligosaccharides in an amount effective to promote the growth of beneficial bacteria. The method is particularly effective for the control of Salmonella species, enteropathogenic Escherichia coli, and Clostridia perfringens.