Salmonella typhimurium (red) invades cultured human cells in this color-enhanced scanning electron micrograph. Credit: Rocky Mountain Laboratories, NIAID, NIH |
A recent discovery of “hypervirulent” Salmonella
bacteria has given University of California, Santa Barbara researchers Michael Mahan and
Douglas Heithoff a means to potentially prevent food poisoning outbreaks
from these particularly powerful strains. Their findings, in a paper
titled “Intraspecies Variation in the Emergence of Hyperinfectious
Bacterial Strains in Nature,” have been published in the journal PLoS Pathogens.
Salmonella
is the most common cause of infection, hospitalization, and death due
to foodborne illness in the U.S. This burden may continue to worsen due
to the emergence of new strains that would tax current health-control
efforts. To address this problem, researchers sought out—and
found—hypervirulent strains that present a potential risk to food safety
and the livestock industry.
An
international team of scientists—which also included Robert Sinsheimer
and William Shimp from UCSB; Yi Xie and Bart Weimer from UC Davis; and
John House from University of Sydney, Australia—conducted a global
search for hypervirulent Salmonella strains. They were found among isolates derived from livestock, and rendered current vaccines obsolete.
Bacteria behave like a Trojan Horse, exposing their weapons only after initiating infection.
“These
strains exhibit this behavior in the extreme—essentially having a ‘5th
gear’ they can switch to during infection,” said Heithoff, lead author
of the paper.
Previous
efforts to find hypervirulent strains were unsuccessful since bacteria
behave much like their less-virulent cousins after environmental
exposure. “The trick was to assess their virulence during
infection—before they switch back to a less-virulent state in the lab,”
said Professor Mahan.
Now
that researchers know what to look for, they are developing methods to
rapidly detect and discriminate the more harmful strains from their
less-virulent cousins. The strategy is aided by a special medium
utilized by the researchers that forces the bacteria to reveal their
weapons in the laboratory—the first step in the design of therapeutics
to combat them.
Humans usually get Salmonella
food poisoning from eating contaminated beef, chicken, or eggs.
However, animal waste can contaminate fields where fruits, nuts, and
vegetables are grown, thus posing a particular health concern for
vegetarians. The threat is exacerbated when these foods are not cooked. Salmonella control efforts are expensive—recent estimates place this cost up to $14.6 billion annually in the U.S.
As
hypervirulent strains pose a potential risk to human and animal health,
mitigation efforts warrant researchers’ careful attention. “Now that we
have identified the problem—and potential solutions—we just need to get
to work,” Heithoff said.
This
research was launched with support from The G. Harold & Leila Y.
Mathers Foundation, which then leveraged additional funding from the
U.S. Department of Agriculture, National Institutes of Health, U.S.
Army, and Santa Barbara Cottage Hospital Research Program.
Intraspecies Variation in the Emergence of Hyperinfectious Bacterial Strains in Nature
