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.
Salmonella enterica 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. Salmonella enterica 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.
Conclusion The Salmonella isolates are within a
major clone and are closely related. The
distribution of the single-nucleotide
polymorphisms appears to be clumped (Figure 1).
Two genes were identified in the region with the
highest number of SNPs. These genes appear to be
regulatory and they may important role in
evolution.
Salmonella genome map
Bin 14
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.
Neuhauser, C. 2007 SNPs and hypothesis testing.
BioQUEST Workshop. South Belloit Reen. F. J. E.
F. boyd, S. Porwollik, B.P. Murphy, D. Gilroy, S.
Fanning and M. McClelland. 2005. Genomic
comparisons of Salmonella enterica Serovar
Dublin, Agona, and Thyphimurium Strains Recently
Isolated from Milk Fliters and Bovine Samples
from Ireland, Using a Salmonella Microarray.
Appl. Environ. Microbiol. 71 1616-1625.
Note According to the simulation, the 95
confidence limit for the ration is 2.15, so this
ratio does not quite exceed that value and
therefore the null hypothesis (that the
distribution is random) cannot be rejected.