接种沙门氏菌苗可使新生雏鸡和强制换羽母鸡得到免疫保护

过去人们常认为,由于刚出壳雏鸡的免疫系统尚未发育成熟,同时肠道内缺乏有益的微生物,因而处于高度的敏感期,此时接种沙门氏菌苗产生的保护作用很有限。然而,最新的研究表明,在这些敏感期接种疫苗,可诱发产生保护作用。     

The Influence of the Housing System on Salmonella Infections in Laying Hens: A Review

From 2012 onwards, housing of laying hens in conventional battery cages will be forbidden in the European Union and only enriched cages and non‐cage housing systems such as aviaries, floor‐raised, free‐range and organic systems will be allowed. Although this ban aims at improving the welfare of laying hens, it has also initiated the question whether there are any adverse consequences of this decision, especially with respect to the spread and/or persistence of zoonotic agents in a flock. A zoonotic agent that is traditionally associated with the consumption of eggs and egg products is Salmonella enteritidis. This paper provides a summary of the current knowledge regarding the direct and indirect effects of different housing systems on the occurrence and epidemiology of Salmonella in laying hen flocks.     

Protection of laying hens against Salmonella Enteritidis by immunization with type 1 fimbriae

Eighteen chickens were immunized subcutaneously with purified type 1 fimbriae from Salmonella enterica serotype Enteritidis at 18 and 21 weeks of age. Evidence of IgG and IgA responses was found in the eggs and in the sera of the immunized hens. Three weeks later, immunized and non-immunized chickens (n=18) were challenged intravenously with 2x10(7) live Salmonella enterica serotype Enteritidis. There was no significant difference in the numbers of eggs laid by immunized and non-immunized birds. The percentage of Salmonella contaminated eggs was significantly higher in the non-immunized group than in the immunized group due to a higher percentage of contamination of the externally disinfected egg shells. There were no statistical differences in the percentages of contaminated yolks and egg whites between control and immunized birds. No differences in the number of colonizing bacteria could be found in the spleen nor in the liver between the immunized and the control groups throughout the experiment. Salmonella was cleared from the ovary of the immunized birds in the second week p.i., in contrast to the control birds where Salmonella was isolated till the third week after infection. Oviducts were significantly more infected in the control group than in the immunized group. Salmonella was cleared from the oviducts at 3 weeks p.i. in the immunized hens but not in the control hens. In conclusion, we demonstrated that the immunization of laying hens with type 1 fimbriae reduced the number of contaminated eggs and reduced the colonization of the reproductive organs.     

Molecular and phenotypical characterization of Clostridium perfringens isolates from poultry flocks with different disease status

Due to the diminished use of growth-promoting antibiotics in the European Union, Clostridium perfringens induced necrotic enteritis and subclinical disease have become important threats to poultry health. A study was set up to genotypically and phenotypically characterise C. perfringens isolates from poultry flocks with different health status. Animals from healthy flocks were sampled by cloacal swabs, while intestinal and liver samples of animals suffering from necrotic enteritis were analysed. A total of 27 isolates was obtained from 23 broiler flocks without clinical problems and 36 isolates were obtained from 8 flocks with clinical problems. Using PFGE typing, high genetic diversity was detected between isolates from different flocks. Isolates derived from flocks where disease outbreaks occurred were clonal within each flock, but each flock harboured a different clone. All isolates were of toxin type A. Isolates from 5 out of 35 PFGE types carried the cpb2 gene, encoding the beta2 toxin, and isolates from 2 out of 35 PFGE types harboured the cpe gene, encoding the enterotoxin. In vitro alpha toxin production for all isolates was quantified by enzyme-linked immunosorbent assay. It was shown that in vitro alpha toxin production of C. perfringens isolates from diseased flocks was not higher than in vitro alpha toxin production from isolates derived from healthy flocks.     

Salmonella enterica serovar Enteritidis colonization of the chicken caecum requires the HilA regulatory protein

Invasion of Salmonella into intestinal epithelial cells is believed to be essential for the pathogenesis of Salmonella infections. Invasion is mediated by genes located on the Salmonella pathogenicity Island I (SPI-1), which are needed for assembling a type three secretion system, that mediates injection of bacterial proteins into the cytosol of epithelial cells, resulting in cytoskeletal rearrangements and as a consequence invasion. HilA is the key regulator of the Salmonella Pathogenicity Island I. To assess the role of hilA in colonization of gut and internal organs in poultry, animals were infected with 10(8) CFU of a delta hilA mutant of S. Enteritidis and its parent strain at day of hatch. Very low numbers of delta hilA mutant strain were able to colonize the internal organs shortly after infection, but they were not eliminated from internal organs at 4 weeks post-infection. At that time, the colonization level of the wild type bacteria in internal organs was decreased to the same low level compared with delta hilA mutant strain bacteria. Shedding of the delta hilA mutant strain and colonization of the caeca was seriously decreased relative to the parent strain starting from Day 5 post-infection. At 4 weeks post-infection, the delta hilA mutant strain was more or less eliminated from the chicken gut, while the parent strain was still shed to a high level and colonized the caeca to a high extent (more than 10(7) CFU/g). It is concluded that hilA is involved in long-term shedding and colonization of S. Enteritidis in the chicken caeca.     

The fibronectin binding protein ShdA is not a prerequisite for long term faecal shedding of Salmonella typhimurium in pigs

Porcine carcasses contaminated with Salmonella typhimurium pose significant public health problems. Prolonged faecal shedding of Salmonella in pigs contributes to the contamination level of carcasses. Although the mechanism of prolonged faecal shedding is not yet clarified, the CS54 Island, and more specifically the shdA gene encoding a fibronectin binding autotransporter protein, was identified as an important locus for intestinal colonization and persistence of Salmonella typhimurium in mice. The aim of this study was to assess the contribution of ShdA in faecal shedding of Salmonella typhimurium in pigs. Pigs were orally inoculated with a Salmonella typhimurium wild type field strain or its isogenic shdA mutant strain. For the first few days after inoculation, the shdA mutant strain was excreted more, the diarrhoea was more pronounced and higher numbers of internal organs were infected. No effect on long-term shedding was found. In a porcine ileal loop model, the wild type strain and shdA mutant strain did not show any differences in the induction of neutrophil influx into the intestinal wall and lumen. In conclusion, we have shown that a Salmonella typhimurium deletion mutant in shdA is more virulent during the first days after inoculation and is not significantly impaired in persistence or prolonged shedding in pigs.     

The Salmonella Pathogenicity Island 2 regulator ssrA promotes reproductive tract but not intestinal colonization in chickens

Using a deletion mutant in the regulator of SPI-2, ssrA, we investigated the role of SPI-2 in invasion, intestinal colonization and reproductive tract infection of chickens by Salmonella Enteritidis. The ssrA mutant was fully invasive in phagocytic and non-phagocytic cells but failed to persist within chicken macrophages. The ability of Salmonella Enteritidis to cause disease in orally infected 1-day-old chicks was not altered when ssrA was deleted. Furthermore, caecal colonization was not affected, while spleen and liver showed reduced colonization. Following intra-peritoneal and intravenous infection of 1-day-old chicks, internal organ colonization was strongly reduced. After intravenous inoculation in adult laying hens bacterial numbers of the ssrA mutant were significantly lower in oviducts and ovaries as compared to the wild type strain. The chickens showed less reproductive tract lesions and the recovery of egg production were faster compared to the wild type strain infected chickens. These findings indicate that the SPI-2 regulator ssrA promotes reproductive tract colonization, but is not essential for intestinal colonization of chickens with the host non-specific serotype Enteritidis.     

Origin of Clostridium perfringens isolates determines the ability to induce necrotic enteritis in broilers

Since the ban on growth-promoting antibiotics in animal feed in the European Union, necrotic enteritis has become a major cause of mortality in broiler chickens. Despite the importance of the disease, the pathogenesis is still not completely understood. In the current study, Clostridium perfringens strains isolated from healthy flocks and isolates from outbreaks of necrotic enteritis were evaluated for the ability to cause gut necrosis in an intestinal loop model in laying hens and in an experimental infection model in broilers. High, intermediate and low alpha toxin producing strains were chosen from each isolation source. Only the isolates from field outbreaks induced necrotic gut lesions, independent of the amount of alpha toxin produced in vitro. It was also shown that alpha toxin producing isolates from calf hemorrhagic enteritis cases were not able to induce necrotic enteritis in poultry. These results suggest the presence of host specific virulence factors in C. perfringens strains, isolated from chickens with intestinal necrotic enteritis lesions.