Staphylococcus aureus is a major human pathogen responsible for a wide diversity of infections ranging from localized to life threatening diseases. Since 1961 and the worldwide emergence and spreading of methicillin resistant Staphylococcus aureus, the bacterium has shown particular capacity to survive and adapt its metabolism to drastic environmental changes. Until recently, Staphylococcus aureus was considered as the prototype of nosocomial pathogen but is now currently responsible for outbreaks in the community. Several recent reports suggest that the epidemiology of MRSA is changing.
The comprehension of pathogenicity, virulence as well as the emergence of epidemic clones within MRSA populations is not clearly understood despite several attempts to identify common feature between populations of strains sharing similar epidemiological or virulence behavior. These studies included pattern profiling of i) bacterial adhesins, ii) clonal complex groups, iii) genotypes based on MLST determination, and iv) enterotoxins content and failed to identify links between clinical isolates.
We hypothesized that predictive parameters contributing to strain virulence or to strain capacity to evolve from non-invasive to invasive character are contained in the genetic material of strains, considering the entire genome. We propose in this application the utilization of massively parallel methods of analysis allowing the study of “genome behavior” based on its content. By using bio-informatics information or tools either publicly available or specifically developed in by our team, we plan to identify single nucleotide polymorphism at the genomic scale, on more than 10 genomes, including at least 6 representative strains sequenced during collaborative efforts. Regions of interest showing particular polymorphism capacity or highly conserved will retain our attention. This evaluation will be performed on the entire genome including ORFs and non-coding sequences. Microarrays developed in our laboratory will allow evaluating at the genome level potential gene expression in regions previously described as intergenic. The same microarray will be used to performed genotyping experiment at the genomic scale on characterized strain collections or groups. Simultaneously, strain collections will be identified by profiting from previous works performed in our laboratory on the basis of i) clonal complex classification, and ii) clinical and epidemiological parameters easily obtainable from our institution database. Pattern of regions of interest previously disclosed by bio informatics and microarray strategies will be identify in our collection of extensively characterized isolates. In vitro screening on groups of isolates will be performed using high throughput tests allowing evaluating capacity of strains to i) produce biofilm, ii) adhere to extracellular matrix proteins, iii) evaluate growth capacity, iv) resistance to killing by neutrophils. Overall, this proposal will contribute to evaluate common features among strain populations, in correlation with their defense and growth capacity. Ideally these determinations will allow to appreciate micro and macro evolution of MRSA and to identify specific genomic markers of their evolution to invasive or highly virulent phenotypes.