A Supplemental Test System to Measure Competitive Exclusion of Salmonellae by Native Microflora in the Chicken Gut

Abstract

An improved individual challenge test system is described for evaluation of competitive exclusion of salmonellae in day-old chicks by native gut microflora. Evaluation of Salmonella protection is based on culture of cloacal and fecal samples by enrichment methods plus enumeration of salmonellae in fresh droppings collected from test groups. The use of a nalidixic-acid-resistant strain of Salmonella allowed for ease of measurement. Comparative data are included that were developed by parallel tests by the seeder bird and this individual challenge test system on Salmonella protection provided by microflora from a specific-pathogen-free population and from intestinal microflora propagated anaerobically in several media. The individual-bird challenge test system appeared to yield more precise measurement of protection than the seeder-bird system. Trypticase soy broth may be as effective as VL broth for anaerobic culture of the protective microflora. Fresh fecal suspensions were somewhat more dependable than anaerobic cultures in providing a high level of protection against subsequent Salmonella infection.