14 | New Scientist | 15 January 2022News Insight
LISTERIOSIS kills hundreds of
people every year in Europe alone.
The bacterium that causes it,
Listeria monocytogenes, can
contaminate all kinds of foods
and keeps growing even in fridges.
But if you live in the US, Canada,
Australia, New Zealand or Israel,
you probably have a lower risk of
infection because you are eating
foods sprayed with a cocktail of
viruses that kill listeria bacteria.
Bacteria-killing viruses, called
bacteriophages, are increasingly
being used to destroy harmful
microbes during food processing,
to stop food rotting and to treat
plant and animal diseases on
farms. One big advantage of thisapproach is that phages can kill
bacteria that have become resistant
to antibiotics or disinfectants.
Bacteriophages are already
everywhere. There are an
estimated 10^31 phages on Earth,
more than every other kind of
biological entity combined. Your
gut alone is thought to hold 10^15.
Given their multitudes, it is
no surprise people have wanted
to put them to work. Phages
have been used to treat human
infections since the 1920s, when
the Eliava Phage Therapy Center
in Tbilisi, Georgia, was set up. It
still treats people today, but phage
therapy is seldom used elsewhere.
It is much easier to prescribe
antibiotics than to find a phage
capable of killing the specific
bacterium infecting a person.
When it comes to food, it is
a different matter. Phages are
increasingly being used in some
countries to kill bacteria that cause
food poisoning. The main targets
are salmonella, shigella and theO157:H7 strain of E. coli, in addition
to L. monocytogenes.
These bacteria can lurk on fresh
foods such as salads and can also
contaminate the surface of foods
after cooking. There is no perfect
way to get rid of them. For
instance, ionising radiation is
extremely effective, but it can alter
the taste, texture and look of food.
When using phages, the usual
approach is to spray a fine mist
containing them over food. This
can be highly effective at killing
unwanted bacteria. Numerous
studies show that it can reduce
bacterial numbers by orders of
magnitude and sometimes even
to the point of undetectability.
Other advantages are that
phages leave no perceptible traces
and have no effects on people,
packaging or machinery, unlike
some of the chemical alternatives
used for disinfecting foods.
They can also be used on organic,
halal and kosher foods. Treated
foods don’t have to be labelled,
as all fresh foods already contain
phages, so packaging can
remain unchanged.Phage cocktail
However, the approach has its
drawbacks too. The main issue is
that each phage targets only one
specific bacterial strain, so a
mixture of phages is required to
kill all the strains that might be
present. This means a cocktail
that proves potent in the US, say,
might not work in other countries.
And because bacteria are always
evolving, the effectiveness of each
phage needs to be constantly
monitored and the mixture
tweaked as necessary.
This can complicate efforts to
obtain regulatory approval, says
Alexander Sulakvelidze, head
of the Maryland-based phage
company Intralytix. Regulatorscountries. “I won’t go so far as
to say phages could be the be-all
and end-all solution.”
Persuading companies to adopt
the technology can also be hard.
“Food processors were somewhat
reluctant to apply viruses on their
food,” says Sulakvelidze.
But many have been won over.
The main motivating factor for
them is avoiding food recalls,
which can cost firms millions.
For instance, in 2009 the Peanut
Corporation of America filed for
bankruptcy after being found to
be the source of a salmonella
outbreak that killed nine people.
Today, Intralytix has five
approved phage products for
killing dangerous bacteria on
human and pet foods, and is
making a profit, says Sulakvelidze.
Several other companies sell
similar products.
Nagel hopes to make such
products available in low-income
countries too. Phages for Global
Health is working with researchersVegetables can be
sprayed with phages
to kill pathogensBiotechnologyMore than just a phage
Bacteria-killing viruses are increasingly being used to clean up our food
and could soon be put to work in healthcare, reports Michael Le Pageare used to dealing with single
chemicals rather than cocktails
requiring constant adaptation,
he says. It took Intralytix more
than four years to get its first
phage product, ListShield,
approved by the US Food and
Drug Administration in 2006.
In addition, because phage
sprays don’t usually kill all
bacteria, their populations can
regrow over time, especially if
food isn’t stored properly. Other
issues include chemicals in or
on foods killing the phages, or the
spray not coating every surface.
For all these reasons, even
phage enthusiasts are cautious
about the claims they make.
“It’s a key tool that could be
added to the toolbox,” says Tobi
Nagel at Phages for Global Health,
a non-profit organisation that
promotes their use in low-income“ One of the biggest issues
with antibiotic resistance
has been the abuse in the
food industry”