East Lansing, Michigan
March 11, 2008Using new
genetic techniques, scientists are unlocking the secrets of how
E coli bacteria contaminate food and make people sick.
Michigan State University has developed a new technique to
test the DNA of E. coli bacteria by examining very small genetic
changes called single nucleotide polymorphisms or SNPs
(pronounced snips). Using SNPs, scientists analyzed 96 markers,
making genetic analysis of pathogenic bacteria possible at a
rate never before accomplished.
“It used to take three months
to score one gene individually,” said Thomas Whittam, Hannah
Distinguished Professor at the National Food Safety and
Toxicology Center at MSU. “Now, we are working on a new, more
rapid system that can do thousands of genes per day.”
In a new study released in the
Monday edition of the Proceedings
of the National Academy of Sciences, “Variation in Virulence
Among Clades of Escherichia coli O157:H7 Associated With Disease
Outbreaks,” Whittam and his co-authors looked at the DNA of more
than 500 strains of a particularly dangerous member of the E.
coli family, O157:H7. In collaboration with David Alland of the
University of Medicine and Dentistry of New Jersey, Whittam
discovered that individual bacteria could be separated into nine
major groups, called clades.
E coli makes people sick
because they produce toxins, called Shiga toxins. These toxins
block protein synthesis, an essential cellular function,
particularly in the kidneys. What Whittam found was that the
different clades produced different kinds of Shiga toxins in
varying amounts based on their DNA.
“For the first time, we know
why some outbreaks cause serious infections and diseases and
others don’t,” Whittam said. “The different E. coli groups
produce different toxins.”
Rapid genetic characterization
also opens up a new world of possibilities for identifying the
bacterial culprits in outbreaks and finding out where they
originated.
E. coli usually come from
animal waste contaminating human sources of food or water.
Finding out how the bacteria entered the food source always has
been a challenge, but now food safety experts can use DNA just
like police use DNA at crime scenes. Scientists will be able to
identify those bacteria making people sick, find out where they
entered the food source and then use this information to reduce
contamination.
“This is the first time anyone
has been able to classify very closely related groups,” Whittam
said.
“This is also the first time we
can tell the differences in how they cause disease.”
Whittam also has plans to use
this methodology to study other bacterial strains, like
Shigella, a major cause of diarrhea around the world. “This new
equipment can be used to identify hundreds of thousands of
pathogenic bacteria,” Whittam said.
The National Institute of
Allergy and Infectious Diseases of National Institutes of Health
through Food and Waterborne Diseases Integrated Research Network
supported this research |
