Studies of the phenomenon of host adaptation in Salmonella

To study the phenomenon of host adaptation in Salmonella, a mathematical mo del has been developed which permits a definition and experimental investig ation of the specific interaction between the adapted serovar and the adequ ate host. After experimental infection using a mixture of equal parts of tw o Salmonella strains, A and B, the bacterial concentrations C-A and C-B wer e determined in the organs of the animals infected. If an animal of species a and an animal of species b are infected with the same mixture of strain A adapted to a and strain B adapted to b, an expression: log(10)Q(ab) = log(10)C(aA) + log(10)C(bB) - log(10)C(aB) - log(10)C(bA) may be calculated which describes the influence of the specific serovar-hos t interaction on the dynamics of the bacterial count. The variable Q(ab) wa s determined using four Salmonella dublin, four Salmonella choleraesuis and five Salmonella gallinarum/pullorum strains in a total of 63 pairs of diff erent hosts (calf and pig, calf and chicken, or pig and chicken). On this b asis, the following statements can be made. The epidemiologically defined h ost adaptation of Salmonellas is accompanied by a specific agent-host inter action between the adapted serovar and adequate host. It promotes adherence and spreading of the agent in the adequate host. The effect was particular ly expressed on day 3 post-infection and could be detected both in the lume n of the anterior sections of the intestine and in the intestinal lymph nod es and the liver. In part, the host-independent strain characteristics had a greater influence than the specific serovar-host interaction on the dynam ics of the bacterial count. Strains of non-adapted serovars may thus result in a more intense colonization and invasion of the host than simultaneousl y administered bacteria of a serovar which is adapted to the respective hos t. The effects of a specific serovar-host interaction on colonization of an d spreading in the host should be considered only as a component which cont ributes to the of host adaptation.