Enterobacteriaceae populations during experimental Salmonella infection in pigs.

Salmonella infection might affect other intestinal Enterobacteriaceae populations and possible correlations between single Enterobacteriaceae populations would help to predict subclinical Salmonella infections in pigs. In one experimental setup, weaned piglets (n=40) were infected with Salmonella and sacrificed at 3h, 24h, 72 h or 28 days post-infection (p.i.). Dilutions of intestinal contents and mucosal tissues were plated on agar plates for determinations of Enterobacteriaceae. In another experimental setup, weaned piglets (n=12) were infected with Salmonella and probed over a period of 28 days p.i., and dilutions of rectal contents were also tested for Enterobacteriaceae populations. The occurrence of single Enterobacteriaceae populations was correlated with the occurrence of other tested Enterobacteriaceae populations as well as with clinical parameters of the piglets. Salmonella (infection strain), Escherichia coli (hemolytic and non-hemolytic) and another six non-E. coli/non-Salmonella Enterobacteriaceae (NENSE) genera with eight species were identified. In general, the absolute numbers of E. coli, Salmonella and NENSE populations decreased with increasing age of the animals. In the jejunum, the numbers of NENSE, E. coli and Salmonella were all highly positively correlated with each other. The occurrence of hemolytic E. coli had no obvious effects on the occurrence of other Enterobacteriaceae. Furthermore, only few associations of Enterobacteriaceae populations with clinical parameters were observed. In conclusion, we did not observe evidences for either a competition between or benefits for specific Enterobacteriaceae populations during Salmonella infection indicating that changes in the composition of the intestinal Enterobacteriaceae microflora are not useful indicators of subclinical Salmonella infections.