Abstract
Investigations were undertaken to quantify the phenomenon of Salmonella host adaptation in certain species. Therefore calves, piglets and chicken were inoculated with suspensions of Salmonella Choleraesuis (S.) (adopted to pigs), S. Dublin (adopted to cattle) and S. Gallinarum/Pullorum (adopted to chicken).
The aim of the study was to answer the question if and in which way Salmonella host specificity is expressed during experimental oral challenges as a result of germ-host-interaction. For this purpose mixtures of cultures of two Salmonella-serotypes ideally containing equal parts of them were used. They were administered simultaneously to two species via oral route. The Salmonella suspension always consisted of an adopted and a non-adopted Salmonella-serotype (S. Choleraesuis x S. Dublin; S. Choleraesuis x S. Gallinarum/Pullorum; S. Dublin x S. Gallinarum/Pullorum). Several samples of small intestine content, gut mucosa as well as extraintestinal tissue (i.e. lymphnodes and liver) were taken for bacteriological counts on day 1, 3, 6 and - in 2 cases - also on day 13 post infection. All samples were homogenized for quantitative reisolation of Salmonella germs applying KOCH´s plate counting. For identification of the different but simultaneously administered Salmonella-serotypes mutants resistant for specific antibiotics were used. To gain general information on serotype-specific attributes we used several Salmonella-strains of each serotype to separate strain-specific attributes from serotype-specific attributes.
Due to the equal ratio of the two administered Salmonella-strains (1:1) it had been possible to quantify a host-specific component by analysing the counts of adopted and non-adopted Salmonella-serotypes. This component is based on a higher growth rate of host adapted serotypes in adequate hosts and therefor traceable by germ counts. The influence of a host-specific component could be demonstrated very clearly in the extraintestinal tissue (lymphnodes) of cattle and pigs, followed by the gut mucosa (mean ratio adopted : non adopted serotypes approximately 15 : 1) and to a smaller extend in the small intestine content. It could be observed in all animal species examined, independent from the number of counted germs.
Along with the investigations the sensitivity of two different methods of tissue sample homogenizing was tested. The Ultra-Turrax(tm) method is characterised by fast rotating knives, while in the Stomacher 80(tm) method the samples are squeezed in sterile plastic bags.
150 samples were homogenized parallely by using both systems. The results show that Stomacher 80(tm) is a very effective method with at least the same or a even better sensitivity compared to Ultra-Turrax(tm). The amount of tissue-collagen may have an influence on the degree of homogenisation.
In vitro tests of simultaneously incubated mixed cultures containing equal parts of two Salmonella-strains showed in almost all cases no interactions. Only strains of S. Gallinarum/Pullorum showed a decreased germ growth rate when incubated together with strains of S. Choleraesuis. The interaction could not be observed before four hours of common incubation. S. Dublin strains showed a similar interaction after ten hours of common incubation. These differences of germ growth rates of strains of S. Gallinarum/Pullorum have proofed to be significant (p < 0,05).
Because of the different body temperature of mammals (37 °C) and birds (42 °C) all tested strains were incubated at 37 °C and 42 °C, but no influence could be noticed for strains of S. Choleraesuis and S. Dublin. Strains of S. Gallinarum/Pullorum showed in some cases a slightly, but not significantly longer germ growth rate at 37 °C incubation temperature.
Summarising the results it can be concluded that under the described conditions Salmonella-suspensions follow the same pattern of growth compared to single incubated strains for at least four hours. Although, in vitro results can not be transferred directly to possible in vivo behaviour it seems to be likely that simultaneously administered Salmonella-strains of equal parts of different serotypes may behave in a similar way. |
