Intestinal colonisation of gnotobiotic pigs by Salmonella organisms: interaction between isogenic and unrelated strains

The effect of intestinal colonisation by a Salmonella strain on the establi shment in the gut of an isogenic mutant administered orally 24 h after the first strain was studied in gnotobiotic pigs, Irrespective of the clinical outcome of the infection, the extensive colonisation of one Salmonella stra in prevented a similar degree of colonisation by an otherwise isogenic anti biotic resistant strain; in some cases the second strain was hardly detecta ble. The poor colonisation of the challenge Salmonella strains was generall y reflected in very low counts of organisms in the tissues. Colonisation by a strain of Escherichia coli reduced the rate of establishment of an isoge nic E. coli, strain but did not prevent colonisation by an S. Typhimurium s train. S. Typhimurium with mutations in the tsr (serine chemotaxis receptor protein) or oxrA (transcriptional regulator of anaerobic metabolism) genes did not inhibit colonisation. Mutations in cya (adenylate cyclase), tar an d trg (chemotaxis receptor proteins for aspartate and ribose respectively) genes were less inhibitory, while motB (non-motile) and cheR (impaired moti lity) mutants were fully inhibitory.