Identification of a new Salmonella enterica serovar Enteritidis locus involved in cell invasion and in the colonisation of chicks.

Poultry products contaminated with Salmonella enterica serovar Enteritidis are a major cause of foodborne disease in industrialized countries. Knowledge of how poultry is colonised is essential for reducing contamination of these products. We have characterized the bacterial yfg-eng locus involved in chicken colonisation. Its sequencing revealed four open reading frames (ORF), yfgM, yfgL, engA and yfgJ, all transcribed in the same orientation. An yfgL mutant of S. Enteritidis colonised the caeca (P < 0.05) and the spleens (P < 0.01) of one-day-old chicks subnormally 2 and 5 days after oral inoculation. This lower virulence was correlated with reduced secretion of the SPI-1 and flagellar proteins in the yfgL mutant compared to the wild-type strain. Consistent with this, the S. Enteritidis yfgL mutant was less motile than the wild type and fewer invaded enterocytes (P < 0.05) and avian HD11 macrophages (P < 0.001). All these defects could be partially overcome by inserting the yfg-eng locus into the mutant on a recombinant plasmid.

Amy M ，Velge P ，Senocq D ，Bottreau E ，Mompart F ，Virlogeux-Payant I ... -  《RESEARCH IN MICROBIOLOGY》

Salmonella enterica serovar Pullorum requires the Salmonella pathogenicity island 2 type III secretion system for virulence and carriage in the chicken.

Functional mutations were made in the type III secretion systems encoded by Salmonella pathogenicity island 1 (SPI 1) and Salmonella pathogenicity island 2 (SPI 2) of Salmonella enterica serovar Pullorum, the cause of pullorum disease in poultry. Their role in cell invasion in vitro, and in virulence in vivo was determined. The SPI 1 mutant showed decreased invasiveness for chicken cells but was capable of causing disease in orally infected 1-day-old chicks, although it showed some reduction in virulence. The SPI 2 mutant showed no reduction in invasiveness, but was fully attenuated for virulence in 1-day-old chicks, and was not detected following oral infection in 1-week-old chickens. Following intravenous infection, the SPI 2 mutant was also attenuated and cleared more rapidly than the parent strain. This indicates that S. Pullorum requires SPI 2 for virulence and persistence but SPI 1 appears to contribute to, but is not essential for, the virulence of S. Pullorum.

Wigley P ，Jones MA ，Barrow PA 《AVIAN PATHOLOGY》

Effect of type 1 fimbriae of Salmonella enterica serotype Enteritidis on bacteraemia and reproductive tract infection in laying hens.

Research on the role of type 1 fimbriae of Salmonella enterica serotype Enteritidis in poultry to date has been focused on the intestinal phase of the infection. This study aimed to investigate the role of type 1 fimbriae in a systemic infection by intravenously inoculating chickens with a fimD mutant or its parent strain. The fimD mutant was present in the blood for 3 weeks after infection, while the wild type parent strain was cleared within the first 3 days. The fimD mutant was isolated at least as much as the parent strain from the liver and spleen for up to 3 weeks after inoculation. The wild type strain was cleared from the caeca in the second week, while the fimD mutant was isolated from the caeca for up to 3 weeks after infection. The ovaries were more heavily infected by the fimD mutant than by the wild-type strain. In the first and second week after inoculation, the oviducts were more frequently infected by the mutant strain. The eggs of birds infected with the fimD mutant were less frequently contaminated with Salmonella. The shells of the eggs were more frequently contaminated by the wild type strain than with the mutant strain. Thus, the absence of type 1 fimbriae prolongs bacteraemia, modifies reproductive tract infection and reduces egg shell contamination by Salmonella enterica serovar Enteritidis.

De Buck J ，Van Immerseel F ，Haesebrouck F ，Ducatelle R ... -  《AVIAN PATHOLOGY》

Deletion of sodCI and spvBC in Salmonella enterica serovar Enteritidis reduced its virulence to the natural virulence of serovars Agona, Hadar and Infantis for mice but not for chickens early after infection.

Salmonella enterica serovars Typhimurium, Enteritidis, Dublin, Choleraesuis or Gallinarum can colonise liver and spleen in particular hosts while infections with serovars Infantis, Agona, Hadar, etc. are usually limited to gastrointestinal tract. Reasons for this behavior are unknown, although it has been shown that sodCI and spv genes exhibit a strict distribution between more and less virulent serovars and they influence Salmonella virulence. However to what extent the presence or absence of these genes is associated with the increased virulence of serovars which possess them has never been addressed experimentally. In this study we therefore first confirmed the exclusive association of spvB and sodCI genes with the former group of serovars. In the next step we removed these two genes from S. Enteritidis genome and compared the virulence of such a mutant with the virulence of S. Infantis, S. Agona and S. Hadar for chickens and highly sensitive Balb/C mice. Single strain infection showed that the deletion of these two genes from S. Enteritidis resulted in the reduction of its virulence for mice but not for chickens. Mixed infection further confirmed these observations and indicated that in mice but not in chickens the virulence of sodCI and spv mutant was reduced to the natural virulence of serovars Infantis, Agona and Hadar. Although sodCI and spv genes do not influence S. Enteritidis virulence for chickens directly, they may be of an indirect effect through the increased persistence of S. Enteritidis in mice and increased probability of the reintroduction of S. Enteritidis into poultry flocks.

Karasova D ，Havlickova H ，Sisak F ，Rychlik I ... -  《-》

Virulence in the chick model and stress tolerance of Salmonella enterica serovar Orion var. 15+.

Three Salmonella enterica serovar Orion var. 15+ isolates of distinct provenance were tested for survival in various stress assays. All were less able to survive desiccation than a virulent S. Enteritidis strain, with levels of survival similar to a rpoS mutant of the S. Enteritidis strain, whereas one isolate (F3720) was significantly more acid tolerant. The S. Orion var. 15+ isolates were motile by flagellae and elaborated type-1 and curli-like fimbriae; surface organelles that are considered virulence determinants in Salmonella pathogenesis. Each adhered and invaded HEp-2 tissue culture cells with similar proficiency to the S. Enteritidis control but were significantly less virulent than S. Enteritidis in the one-day-old and seven-day-old chick model. Given an oral dose of 1 x 10(3) cfu to one-day-old chicken, S. Orion var. 15+ isolates colonised 25% of liver and spleens examined at 24 h whereas S. Enteritidis colonised 100% of organs by the same with the same dose. Given an oral dose of 1 x 10(7) cfu at seven-day old, S. Orion var. 15+ failed to colonise livers and spleens in any bird examined at 24 h whereas S. Enteritidis colonised 50% of organs by the same with the same dose. Based on the number of internal organs colonised, one of the three S. Orion var. 15+ isolates tested (strain F3720) was significantly more invasive than the other two (B1 and B7). Also, strain F3720 was shed less than either B1 or B7 supporting the concept that there may be an inverse relationship between the ability to colonise deep tissues and to persist in the gut. These data are discussed in the light that S. Orion var. 15+ is associated with sporadic outbreaks of human infection rather than epidemics.

La Ragione RM ，Coles KE ，Jørgensen F ，Humphrey TJ ，Woodward MJ ... -  《INTERNATIONAL JOURNAL OF MEDICAL MICROBIOLOGY》