Why only particular animal species are infected by Salmonella?

You may know that many strains of Salmonella bacteria are specific to certain species of animals. Some of them may infect cows, pigs, chickens or sheep, still others infect primarily humans. Recently, a study by a team of scientists from University of Pennsylvania showing that slight variations in the coding sequence of proteins that bind Salmonella to host cells can determine what type of animal a particular strain infects. The findings were gotten using genomic techniques. The team first focused on the analyses of Salmonella enterica serovar Typhimurium, a leading cause of food poisoning. But it is still a mystery for which the molecular basis for host preferences is. Single nucleotide polymorphisms (SNPs), variations in the nucleotide sequence of DNA, were identified through the genomic analyses. They found a relatively large number of SNPs, in genes coding for Salmonella surface proteins or secreted factors. Different host species would share patterns of these so-called non-synonymous SNPs, creating different protein sequences and structures. Through analyzing of 15 genes in 580 strains of Typhimurium, the team found a high degree of variation and evidence of positive selection and strong evidence that the variation was associated with the particular strains' host specificity. Further research will be conducted to determine the genetic differences that may separate a strain of Salmonella that causes a brief gastrointestinal illness from one that cause a major systemic disease. The study was published in the Nature Communications. You may like this>>>http://www.cusabio.com/Recombinant-Protein/Recombinant-Homo-sapiens-Human-T-cell-surface-glycoprotein-CD8-alpha-chain-11090032.html