Broiler lines divergently selected for digestive efficiency also differ in their susceptibility to colibacillosis.

Increasing feed efficiency of broiler chickens by selective breeding could lead to decreased feed cost and reduced environmental impact of poultry production. At INRA, two broiler chicken lines (D+/D-) were divergently selected for their digestive efficiency. Strong differences were shown between both lines for the anatomy and histology of the digestive tract, and for the intestinal microbiota composition. In the present study, we investigated whether this selection also had an effect on susceptibility to colibacillosis, which is one of the main causes of economic losses in poultry production. The broiler lines D+/D- were challenged with an avian pathogenic Escherichia coli strain. A first experiment was conducted to assess the 50% lethal dose by subcutaneous infection of hatchlings, whereas a second experiment reproduced colibacillosis by infecting air sacs of 23-day-old chicks. The 50% lethal dose was very low for both lines. However, the line with the higher digestive efficiency (D+) was the less susceptible to colibacillosis. This result is interesting for selection purposes and opens the way to integrative genetic studies of the interactions between digestion efficiency and resistance to colibacillosis.

Tissues and cells involved in the invasion of the rabbit intestinal tract by sporozoites of Eimeria coecicola.

This study was designed to identify an extra-intestinal route of migration of Eimeria coecicola sporozoites and the types of cell harbouring the parasite during the invasion of the intestine. The presence of E. coecicola in blood, spleen and mesenteric lymph nodes of infected donor rabbits was demonstrated by immunohistology on donor organs and measurement of oocyst excretion by coccidia-free recipient rabbits injected with whole-cell suspensions prepared from donor tissues. Two types of donor lymphocyte, B (IgM+) and T (CD5+), were labelled using a two-colour immunofluorescence-labelling technique and separated with a cell-sorter (FACStar(Plus)). The presence of parasites in the sorted cells was assessed by direct examination and by using the same in vivo test after intravenous injection of IgM+ B or CD5+ T lymphocytes collected from donors at different times after inoculation. This test provided evidence that the parasites were alive and still infectious within the sorted lymphocytes. It was demonstrated that both B and T lymphocytes were infected.

Natural transmission of Pneumocystis carinii in nonimmunosuppressed animals: early contagiousness of experimentally infected rabbits (Oryctolagus cuniculus).

Airborne transmission of Pneumocystis carinii has been established, but the infective form and the sources of infection remain unknown. Animal models for studies of P. carinii have previously been limited to immunosuppressed rodents; however, this study was performed with nonimmunodepressed P. carinii-free rabbits. This study was aimed at determining (i) the delay between inoculation of animals (day zero [D0]) and the onset of contagiousness and (ii) the end of contagiousness of these animals (donors). Five-week-old rabbits were used as contact animals and were housed with the donors. The cohabitation periods were for 4 or 5 days from D0 to D4, D4 to D8, D8 to D13, D13 to D18, and D18 to D22. The highest parasite burdens were observed in contact animals housed with donors from D8 to D13 or D13 to D18. This period (8th to 18th day following the day of inoculation of donors) might correspond to the highest phase of contagiousness of donors.

Serological conservation and location of the adhesin of avian Escherichia coli type 1 fimbriae.

By inoculation of mice with purified type 1-like fimbriae isolated from an avian Escherichia coli strain, a monoclonal antibody (mAb G5) was obtained. mAb G5 reacted in an enzyme-linked immunosorbent assay (ELISA) with type 1-like and type 1A fimbriae differing in the molecular masses of their major fimbrial subunit and isolated from several avian E. coli strains. The specificity of mAb G5 for type 1 fimbriae was assessed in a whole bacteria ELISA with 16 reference E. coli strains expressing different types of fimbriae. Immunoblotting experiments showed that mAb G5 recognized the 29 kDa minor component of reference type 1A fimbriae which has been identified as the adhesin. mAb G5 also recognized the 29 kDa component of type 1-like and type 1A fimbriae expressed by avian E. coli strains, suggesting that the adhesin is antigenically conserved among these fimbriae. Immunoelectron microscopic studies gave evidence that the adhesin could be located mainly at the tip or both at the tip and along the fimbriae, depending on the strain.