Current concepts of competitive exclusion cultures for the control of salmonellae in domestic poultry

Two defined competitive exclusion (CE) cultures (CF-I and CF-II) and a characterized CE culture (CF-III), which are composed of mixtures of nonpathogenic bacteria, were developed from anaerobic continuous-flow (CF) cultures that had been inoculated with cecal contents from adult chickens. After the primary CF cultures attained homeostasis, 13 bacteria (11 facultative anaerobes and 2 obligate anaerobes) representing 6 genera were isolated from CF-I; II bacteria (9 facultative anaerobes and 2 obligate anaerobes) representing 7 genera were isolated from CF-II; and 29 bacteria (15 facultative anaerobes and 14 obligate anaerobes) representing 14 genera were isolated from CF-III. Newly hatched chicks were treated orally with each primary CF culture; challenged on day 3 with Salmonella typhimurium; and cultured on day 10. Each culture significantly (p < 0.05) reduced salmonellae intestinal colonization and organ invasion. From the reconstituted CF-I and CF-II cultures, all organisms were isolated and their fermentation parameters and efficacy against salmonellae challenge were similar, if not identical, to the primary cultures. The CF-I and CF-II cultures satisfied the 5 requirements for defined CE cultures: 1) the primary CE culture must be efficacious; 2) all bacteria must be isolated and identified; 3) the fermentation parameters of the reconstituted CE culture must be similar to those of the primary culture; 4) all bacteria from the reconstituted culture must be isolated and identified; and 5) the efficacy of the reconstituted culture must be very similar to the primary culture. From these integrated studies, 3 mechanisms were demonstrated for preventing the enteric colonization of salmonellae in newly hatched chicks that were pretreated with CE cultures. First, the component organisms in the CE culture establish a normal enteric flora prior to salmonellae exposure. Second, the CE organisms compete with salmonellae for essential nutrients. Third, the CE organisms produce concentrations of volatile fatty acids at low pH levels that are bacteriostatic for salmonellae.