MICROBIOLOGY FEATURE
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• Residue management
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PHAGE
Studies focused on the
utilisation of viruses that
infect and kill bacteria
- known as bacteriophages or
phages - in preventing infectious
diseases has found that each
individual bacteriophage only
infects a handful of bacterial
species or strains, which makes
them veritable weapons of
precision in the prevention of
bacterial diseases. Study head
Professor Mikael Skurnik - in
cooperation with researchers at the
Seoul National University in South
Korea – has focused on the Yersinia
enterocolitica bacterium, by far the
most common cause for yersiniosis
which is usually transmitted
through raw or undercooked
pork, or less commonly
through milk and contaminated
kitchenware. Skurnik found four
bacteriophages that infect the Y.
enterocolitica bacterium – the most
effective of this quartet the fHe-
Yen9-01 phage which was tested
for its efficacy in decontaminating
food and kitchenware contaminated
by bacteria. “We focused on
those foodstuffs that most often
transmit infections, as well as
those kitchen utensils most often
used to handle these foodstuffs,”
he says. Everyday products
available in grocery shops, such
as raw and grilled pork as well
as milk, were inoculated with Y.
enterocolitica. The contaminated
food was then subjected to phage
treatment, after which the number
of both bacteria and phages was
monitored for three days. “Phage
treatment was effective in inhibiting
bacterial growth in food, while
the number of phages in the food
grew, indicating that phages
infect bacteria and grow in them
also when refrigerated,” Skurnik
says. Researchers then inoculated
Clostridium difficile – a deadly
infection increasing in prevalence
around the world – has been linked
to the widely-used food additive
trehalose by Baylor College of
Medicine researchers. In laboratory
tests and animal models, trehalose
has been found to affect the virulence
of epidemic C. difficile lineages that
predominate in patient infections.
Study head Dr Robert Britton says
in 2000, trehalose was approved as
a food additive in the United States
for a number of foods from sushi
and vegetables to ice cream, and
about three years later the reports of
outbreaks with these lineages started
to increase. “Other factors may also
contribute, but we think that trehalose
is a key trigger,” he says. “An
important contribution of this study
is the realisation that what we once
considered a perfectly safe sugar
for human consumption can have
unexpected consequences. Our study
suggests that the effect of trehalose
in the diet of patients in hospitals with
RT027 and RT078 outbreaks should
be further investigated.” In 2015,
C. difficile caused almost 500,000
infections in patients and 29,000
estimated deaths. The bacteria
cause life-threatening inflammation
of the colon and diarrhoea, with
patients 65 years and older most at
risk. Resistance to fluoroquinolone
antibiotics is likely to be one of the
factors that is helping the lineage
cause epidemics, but researchers
were suspicious that other factors
were also present. Britton says they
discovered that these lineages can
grow on levels of sugar trehalose
that are about 1000 times lower
than those needed by other lineages
of these bacteria. Each lineage is
highly efficient at using trehalose and
evolved independent mechanisms
to utilise this sugar. Further
experiments with mice showed
that increased disease severity in
the presence of trehalose could
not be explained by having higher
numbers of bacteria. “These and
other experiments provide evidence
that dietary trehalose has contributed
to the predominance of epidemic C.
difficile lineages and to their
virulence.”
BREAKTHROUGH
Ready for the next food additive? University
of Helsinki researchers reckon bacteria-killing
viruses can be employed in the food industry
to eradicate foodborne pathogens and prevent
FOOD ADDITIVE food poisoning.
THE BAD GUY
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