Significance of motility of Salmonella enteritidis and Salmonella typhimurium as a virulence factor and on the expression of the inhibition phenomenon in vitro and in vivo in SPF chickens

Methods of immunoprophylaxis for poultry using live Salmonella vaccines are increasingly gaining in importance. Methods of a simple and reliable bacteriological as well as serological differentiation between vaccine and field strains will be of decisive importance for the acceptance and use of live Salmonella vaccines. The absence of motility in Salmonella strains may be a marker fulfilling these criteria. The studies described served to examine whether virulence and the ability to inhibit other Salmonella strains could be influenced by the absence of motility in Salmonella (S.) Enteritidis and (S.) Typhimurium. In a cell-culture model (IEC 6) under in vitro conditions, non-motile transposon mutants (TnphoA) of S. Enteritidis and S. Typhimurium exhibited a clearly reduced invasion potential in comparison with the respective motile parental strain. Under in vitro conditions (nutrient broth culture), the inhibitory potential of these non-motile mutants was also reduced compared to the motile original strains. In contrast, in vivo studies in a-few-days-old chickens revealed that there was no reduction of the virulence of non-motile mutants of S. Enteritidis and S. Typhimurium in comparison with the motile parental strain. In day-old chicks, the inhibitory potential of non-motile strains was significantly reduced and in some cases, had even become completely lost.