June 2021 - 9

CPS continues to fund research into listeria
By Stephen Kloosterman
Associate Editor
Unless one counts Korean-grown
Enoki mushrooms, the U.S. Centers
for Disease Control have not tied fruits
or vegetables to a major outbreak of
listeria infections since 2016.
And yet, the pathogen is deadly
enough to merit further study by the
produce industry. While salmonella
and E. coli foodborne illness have
higher numbers of outbreaks and
individual cases, Cornell University
professor Martin Wiedmann said the
number of deaths due to listeria is the
same or higher.
" If you have an outbreak or even a
case, it's much more likely that people
die, and it tends to be even more severe
than E. coli. Ninety percent of people
with listeria end up in the hospital, and
15-20% of people die, " Wiedmann said.
" So, it's very, very severe - what makes it
worse is, some of these severe cases are
actually abortions in pregnant women. "
" Once a year, bring in
someone independent to
almost be fake FDA in terms
of taking samples like FDA
works, so you're prepared
and you know where your
weaknesses are. "
− Martin Wiedmann,
Cornell University
Wiedmann, a specialist in food
science, will present at the Center for
Produce Safety's (CPS) virtual research
symposium this summer. CPS in 2020
had funded Wiedmann's research
evaluating prioritizing different
interventions for produce processing
plants. It also recently funded a study
looking at the effectiveness of listeria's
resistance to hand sanitizer by Xiangyu
Deng of the University of Georgia.
Uncanny survival
Of concern to the produce industry
is listeria's " uncanny " ability to live
in food processing facilities for long
periods of time - as much as 10-15
years, Wiedmann said. Listeria can
live in the difficult-to-clean areas of
machinery or cracks of the processing
plant floor, infecting only a small
percentage of the total product.
But with modern DNA profiling
of the bacteria, the CDC is able to
match several cases occurring over
a long period of time, and it then
would initiate an investigation with
interviews. Eventually, in such an
investigation, CDC would visit a
business conducting what's known
in the industry as a " swab-a-thon " -
taking dozens of samples around the
processing plant to look for pathogens.
Wiedmann distinguishes between the
" For listeria to cause an issue, it
Cornell University professor Martin Wiedmann studies the impact of listeria on food
safety. Photo: Cornell University
public health risk and the business risk.
" If (the Food and Drug Administration)
or your customer finds listeria on your
product, your apples, that's a recall, and
then that brings all the negative business
consequences, " he said.
Different approaches
Companies use a variety of different
approaches to mitigate risk. Some have
staff or a third-party stage their own
swab-a-thons to check if procedures
work.
" That's a very valuable strategy, "
Wiedmann said. " Once a year, bring in
someone independent to almost be fake
FDA in terms of taking samples like
FDA works, so you're prepared and you
know where your weaknesses are. "
While sanitizers are part of food
safety, Wiedmann said it's possible
to overspend on sanitizer products,
especially if they aren't reaching cracks
or inside machinery where the bacteria
may be living.
" You're spending your money on
biofilm-busting technology, when
you really should take that money
and spend it on redesigning your
equipment, or hiring another person
on your sanitation shift, so you can take
apart that equipment so you can reach
the spots where the sanitizer doesn't
reach it, " he said. " Sometimes cleaning
equipment doesn't work. Sometimes
you have to come up with something
else. ... I think in terms of sanitary
equipment design we can learn a lot
from the meatpacking industry. "
Wiedmann advocates that processing
facilities develop programs and train
staff to conduct " root cause analysis " to
determine where listeria is coming from
or hiding out, and then prioritize which
of those root causes to first address.
Case studies
One outbreak of listeriosis in 2014
was linked to commercially produced,
prepackaged caramel apples.
" In general, apples are acidic enough,
and just don't support growth of
listeria, " he said. " What had happened
with caramel apples is, (when) you stick
this wooden stick into the core, you
essentially created an environment that
allowed the listeria to grow. "
For listeria on a food item to reach
a level of toxicity causing death or an
abortion, it usually has to grow for
some time, Wiedmann said.
needs to be on the food, but then it
needs to grow on the food, " he said. " It
needs to grow to high enough numbers
so there is a risk of making someone
sick. This whole idea of grow/not grow
is very clear if you look at the types of
foods that cause issues. ... All these
things are stored at refrigeration-level
temperatures long enough that listeria
can grow. "
For his research funded by
CPS, Wiedmann and co-principal
investigator Renata Ivanek, also
of Cornell, dove into some 1,656
documents looking for what sorts
of listeria-fighting interventions or
strategies worked best. After narrowing
the group down to 264, the team
further screened them to identify about
32 of the most relevant strategies. They
then validated some interventions
they identified with four cooperating
packinghouse facilities.
Wiedmann's presentation at the CPS'
virtual research symposium this summer
will contain a lot of real-world examples.
" I'm a scientist, and it's all about the
science, right? But, sometimes the stories
you can tell about individual facilities -
obviously anonymously - what issues you
find can help people to see their facilities
in a different light. " VGN
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June 2021

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