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-Selection for increased resistance to Salmonella colonisation and excretion could reduce the risk of foodborne Salmonella infection. In order to identify potential loci affecting resistance, differences in resistance were identified between the N and 6 1 inbred lines and two QTL research performed. In an F2 cross, the animals were inoculated at one week of age with Salmonella enteritidis and cloacal swabs were carried out 4 and 5 wk post inoculation (thereafter called CSW4F2 and CSW4F2) and caecal contamination (CAECF2) was assessed 1 week later. The animals from the (N × 6 1 ) × N backcross were inoculated at six weeks of age with Salmonella typhimurium and cloacal swabs were studied from wk 1 to 4 (thereafter called CSW1BC to CSW4BC). A total of 33 F 2 and 46 backcross progeny were selectively genotyped for 103 and 135 microsatellite markers respectively. The analysis used least-squares-based and non-parametric interval mapping. Two genome-wise significant QTL were observed on Chromosome 1 for CSW2BC and on Chromosome 2 for CSW4F2, and four suggestive QTL for CSW5F2 on Chromosome 2, for CSW5F2 and CSW2BC on chromosome 5 and for CAECF2 on chromosome 16. These results suggest new regions of interest and the putative role of SAL1.

-Selection for increased resistance to Salmonella colonisation and excretion could reduce the risk of foodborne Salmonella infection. In order to identify potential loci affecting resistance, differences in resistance were identified between the N and 6 1 inbred lines and two QTL research performed. In an F2 cross, the animals were inoculated at one week of age with Salmonella enteritidis and cloacal swabs were carried out 4 and 5 wk post inoculation (thereafter called CSW4F2 and CSW4F2) and caecal contamination (CAECF2) was assessed 1 week later. The animals from the (N × 6 1 ) × N backcross were inoculated at six weeks of age with Salmonella typhimurium and cloacal swabs were studied from wk 1 to 4 (thereafter called CSW1BC to CSW4BC). A total of 33 F 2 and 46 backcross progeny were selectively genotyped for 103 and 135 microsatellite markers respectively. The analysis used least-squares-based and non-parametric interval mapping. Two genome-wise significant QTL were observed on Chromosome 1 for CSW2BC and on Chromosome 2 for CSW4F2, and four suggestive QTL for CSW5F2 on Chromosome 2, for CSW5F2 and CSW2BC on chromosome 5 and for CAECF2 on chromosome 16. These results suggest new regions of interest and the putative role of SAL1.

Quantification of the carrier state of Salmonella enteritidis in chicks (i.e., persistent asymptomatic association of S. enteritidis with the host), should provide an optimized means for further investigations into this problem. We therefore developed an experimental carrier state model by oral inoculation of low doses (10(2)-10(4)) of S. enteritidis in B13 chicks at different ages. Liver, spleen, and ceca colonizations by the challenge strains were measured weekly by enumeration of S. enteritidis colony-forming units (CFU) for 7-12 weeks. High mortality rates, incompatible with the carrier state, were observed in chicks inoculated with 10(2) organisms of either a parental strain of S. enteritidis (5556) or a mutant resistant to streptomycin (Smr) and nalidixic acid (Nalr) (strain 1009) at 1 day old. Both strains colonized organs similarly, allowing us to use subsequently the SmrNalr mutant strain. The selected low doses of S. enteritidis induced no deaths in chicks inoculated at 1 or 3 weeks of age. However, inoculation of 3-week-old chicks did not induce a satisfactory carrier state; organ colonization by S. enteritidis was weak and transient, even after inoculation of 10(8) SE. In contrast, some birds infected at 1 week of age presented the challenge strain in the liver and spleen for 3 weeks after inoculation and in the ceca for 12 weeks postchallenge. Most of these birds were colonized by S. enteritidis in the liver and in the ceca for 3 weeks and 10 weeks, respectively, following inoculation. Generally, CFU levels were highest during the first week(s) after inoculation and then decreased progressively. Levels of S. enteritidis were lower in the liver and spleen than in the ceca. Oral inoculation of 1-week-old birds with 5 x 10(4) S. enteritidis provided the required model, allowing quantification of the carrier state of S. enteritidis in chicks.