Evolution within Australian Salmonella strains

1. Evolution within Australian Salmonella strains Mark Bergland, Karen Klyczek, Arlin Toro and Dinitra White Introduction Salmonella is a Gram-negative, cylindrical rod of approximately 2 – 0.5 microns. Salmonellaenterica serovar Typhimurium multiplies in the gastrointestinal tract of many animal species where it usually persists with out causing disease, however in humans its growth may result in gastroenteritis. Six to 48 hours following ingestion of contaminated food or water, nausea and vomiting often occur followed by diarrhea. The disease is usually self-limiting in healthy adults, but may be more serious in children and the elderly with underlying medical conditions. Modern methods of animal husbandry, food preparation and distribution has resulted in the increase of gastroenteritis in humans in recent years. Salmonellaenterica serovar Typhimurium grows in the gut of almost all animals, both domesticated and wild. The S. enterica serovar Typhimurium strain LT2 was isolated in the 1940s. The complete circular genome 4,857 kb and is has been reported in Nature 413: 852-457 (2001). The strains of Salmonella enterica serovar typhimurium used in this study are isolates from bovine, chicken, emu, human, porcine, alpaca, feline, snake and goat samples in different regions of Australia. Salmonella genome map Methods Using the data from the Hu et al (2006) paper, we analyzed the SNP distribution across the Salmonella genome in Excel (Neuhauser 2007). We sorted identified SNPs into bins of 250,000 nucleotides each, and determined the average number of SNPs in each bin. Genes that were located in a region with a higher SNP number were investigated. Fig. 1. Chromosomal distribution of SNPs. Bin 1 corresponds to nucleotides 1-250,000, bin 2 corresponds to nucleotides 250,0001-500,000, etc. The average number of SNPs in each bin and the variance were calculated, and the ratio of variance to mean indicates that the distribution may be clumped rather than random.