Genetic differences among Staphylococcus aureus isolates from dairy ruminant species: a single-dye DNA microarray approach.

Staphylococcus aureus is recognized worldwide as a major pathogen causing clinical or subclinical intramammary infections in lactating sheep, goats and cows. The present study was carried out to compare 65 S. aureus isolates mainly obtained from nasal carriage and subclinical mastitis in dairy sheep and 43 isolates obtained from subclinical mastitis from 22 goats and 21 cows. A DNA microarray, containing probes against 190 true or putative virulence factors, was used to detect the presence of the virulence genes. Their presence/absence was independently assessed by PCR for the genes of interest. Sheep isolates obtained from the nostrils or the udders did not show any significant tissue specific virulence factor. The dominant pulse-field electrophoresis profile (OV/OV'), associated with spa clonal complex spa-CC 1773, matched mainly with the agr group III and was only found in ovine and caprine isolates. This clone was more specifically characterized by the prevalence of the following virulence genes: lpl4, ssl6, bsaA1, bsaB, bsaP, SAV0812. Moreover, seven virulence-associated genes (lpl1, sel, sec, tst, lukF-PV-like component, lukM, SAV0876) were associated with isolates from small ruminants, while the egc cluster, fhuD1, abiF and SAV2496 with bovine isolates. This genomic study suggests the existence of lineage- and host-specific genes leading to the development of host-specific pathogenic traits of S. aureus isolates.

Gene expression profiling of human liver transplants identifies an early transcriptional signature associated with initial poor graft function.

Liver ischemia-reperfusion injury occurring in orthotopic liver transplantation (OLT) may be responsible for early graft failure. Molecular mechanisms underlying initial poor graft function (IPGF) have been poorly documented in human. The purpose of this study was to identify the major transcriptional alterations occurring in human livers during OLT. Twenty-one RNA extracts derived from liver transplant biopsies taken after graft reperfusion were compared with 7 RNA derived from normal control livers. Three hundred seventy-one genes were significantly modulated and classified in molecular pathways relevant to liver metabolism, inflammatory response, cell proliferation and liver protection. Grafts were then subdivided into two groups based on their peak levels of serum aspartate amino transferase within 72 h after OLT (group 1, non-IPGF: 14 patients; group 2, IPGF: 7 patients). The two corresponding data sets were compared using a supervised prediction method. A new set of genes able to correctly classify 71% of the patients was defined. These genes were functionally associated with oxidative stress, inflammation and inhibition of cell proliferation. This study provides a comprehensive picture of the transcriptional events associated with human OLT and IPGF. We anticipate that such alterations provide a framework for the elucidation of the molecular mechanisms leading to IPGF.