Quantification of Experimental Salmonella enteritidis Carrier State in B13 Leghorn Chicks

Abstract

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.

A genome scan for quantitative trait loci affecting the Salmonella carrier-state in the chicken

“…Resistance at one week of age of a total of 99 one-week-old-chicks was assessed 5 weeks after oral inoculation of one-week-old-chicks with 5×10 4 cfu of Salmonella enteritidis (SE) strain 1009 [15]. Between 5 and 7 chicks per line were slaughtered each week until 7 weeks post inoculation and their total caeca cultured for Salmonella, before and, when the results were negative, after enrichment.…”

“…In the F 2 data set, a total of 186 progeny were reared from a (N × 6 1 ) × (N × 6 1 ) cross and inoculated as formerly described ( [15] and Sect. 2.1).Three phenotypic measurements were used in QTL mapping analyses: CSW4F2 and CSW5F5, i.e.…”

“…a better ability of the animals to clear Salmonella), which can be measured by the persistency of the bacterial infection after inoculation. In order to address this question, experimental models of infection were defined in chicks [15] and adult hens [31]. By using these models, the heritability of resistance was estimated at 0.20 in young birds [4] and more than 0.35 in laying hens [2].…”

Cell invasion of poultry-associated Salmonella enterica serovar Enteritidis isolates is associated with pathogenicity, motility and proteins secreted by the type III secretion system

“…S. Enteritidis is also invasive in both young and adult chickens. Young chickens less than 2 weeks of age often develop systemic disease with varying degrees of mortality (Duchet-Suchaux et al, 1995;Suzuki, 1994;Velge et al, 2005) whereas most adult hens colonized with S. Enteritidis become intestinal carriers and typically remain asymptomatic (Golden et al, 2008;Lister, 1988;Velge et al, 2005). S. Enteritidis can invade internal organs of laying hens and infect reproductive tissues leading to internal contamination of newly formed eggs (De Buck et al, 2004;Guard-Petter, 2001;Velge et al, 2005).…”

Use of Integrated Studies to Elucidate Potential Benefits from Genetic Resistance to Salmonella Carrier State in Fowl

“…Guillot et al, (1995) observed differences in response to inoculation of chickens with a high bacterial dose. To mimic carrier-state in chicks, Duchet-Suchaux et al, (1995) developed a protocol of experimental inoculation where animals were orally infected with a low dose, showed no symptom but remained infected for several weeks. They could thus identify genetic models for further research, both outbred (Duchet-Suchaux et al, 1997) and partially inbred lines (Tilquin et al, 2005).…”