Interference between Escherichia coli genotypes from the E. coli peritonitis syndrome given simultaneously to productive SPF White Leghorn hens by intratracheal inoculation.

The purpose of the present study was to examine if potentiation of mortality occurred after simultaneous administration of several Escherichia coli genotypes, each capable to induce the E. coli peritonitis syndrome, in comparison with single genotype application. Five groups of productive Specified Pathogen Free White Leghorn hens were housed in isolators. Groups 1-4 consisted of 32 hens each, Group 5 of 10 hens. At 32 weeks of age all groups were inoculated intratracheally. Groups 1 and 2 were inoculated with a mix of 4 E. coli genotypes, groups 3 and 4 with a mix of 4 other genotypes. Groups 1 and 3 were given 1 median lethal dose (LD 50 ) of each genotype per hen, groups 2 and 4 a dose of 0.1 LD 50 per genotype per hen. Group 5 was mock inoculated. The experiment ended one week after inoculations. In Group 5, no mortality occurred and gross lesions were absent at post-mortem examination. Mortality in groups 1 and 3 was 84% and 81%, respectively; in groups 2 and 4 59% and 66%, respectively. Although mortality in groups 1 and 3 exceeded the expected 50%, this could not be due to potentiation as cluster analysis of reisolates showed that in individual hens only one genotype was found, indicating interference between E. coli genotypes. In groups all four or only two genotypes were recovered, showing that not all genotypes will induce colibacillosis in all experimental groups. Therefore, broad protection can be best assessed challenging with various single genotypes.Research highlights All 4 or 2 E. coli genotypes were found in groups of hens given mixes of 4 genotypes.In contrast, in individual hens only one genotype was found. E. coli genotypes interfere with each other in hens after given as mix.Interference is likely based on a random process.Broad protection can best be assessed challenging with single genotypes.