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Listeria: Craftier Than
First Believed
 AUBURN, Feb. 10, 2004
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Until now, scientists knew listeria was a serious
pathogen; they just didn’t know how serious.
As it
turns out, listeria is one crafty pathogen – craftier
than they ever imagined. And adaptive. And tenacious.
Scientists have discovered the wily bacteria can grow
and reproduce even in the acid conditions of the gall
bladder. It also can survive outside cells and in the
liver.
From
the standpoint of food safety, that’s not good, said Dr.
Jean Weese, an Alabama Cooperative Extension System food
scientist and Auburn University associate professor of
nutrition and food science. It means food handlers who
don’t wash their hands regularly or adequately can
spread it to others, even though they may not experience
the first symptom of listeriosis, the condition
associated with exposure to the pathogen. This raises
the frightening specter of Typhoid Mary, the hapless
carrier of typhoid fever who left scores of people sick
and dead in her wake in the late 19th and
early 20th centuries.
It’s
especially bad news for immuno-compromised people ---
AIDS and diabetes sufferers, the very young and the very
old.
While
the most recent findings have instilled them with an
even better understanding of the pathogen’s resilience,
scientists have long held a grudging appreciation for
listeria’s dogged persistence.
“What
really makes listeria such a serious pathogen is that,
unlike other common pathogens such as salmonella and
E.coli O157:H7, it can be airborne,” Weese said.
“The
bacteria don’t have to be spread entirely through
touching. It can be anywhere in this room --- not only
in the air but on the floor and even on people,” she
said, drawing an arc with her index finger.
Among
foods, it is most commonly found in unpasteurized milk,
soft-ripened cheeses and ready-to-eat meats, such as hot
dogs and pate. That explains why there has been such a
heightened awareness about lunch meat safety within the
last few years. Other sources of listeria include raw
and cold-smoked fish, raw meats and poultry, cooked
poultry, fresh vegetables and ice cream.
“Because these meats are exposed to air during
processing, there’s the chance that some of these
pathogens can attach to them. And listeria can
continue growing even after virtually all of the air has
been vacuumed out in the course of packaging.”
Once
the meat is opened and placed in the refrigerator, the
bacteria multiply even more, she said.
“It’s
almost like the proverbial rabbit in the briar patch,”
Weese said. “You’ve give it two of the conditions in
which it thrives --- low-oxygen environments and colder
temperatures.”
The
detection of listeria
in a meat product at an Atlanta supermarket
recently prompted Vincent Giordano Corp. of Philadelphia
to recall about 52,000 pounds of beef. Georgia health
officials detected the pathogen on a deli meat product
in a Kroger delicatessen counter.
Immune
compromised people need to be especially careful, Weese
said.
“If you
have someone who is susceptible and they’re eating lunch
meats, you need to microwave them before serving,” she
said. “Just heating the food in the microwave at very
low temperatures will kill listeria.”
Cheese
included in the lunch packet should be prepared the same
way, she said.
“Yes, I
know among some people think this defeats the whole
purpose of luncheon meats since they are supposed to be
cold, but if you’re dealing with an immuno-compromised
person, you can’t take any risks.”
[Source: Dr. Jean
Weese, Alabama Cooperative Extension System Food
Scientist and
Auburn
University
Associate Professor of Nutrition and Food Science,
334-844-3269: Jim
Langcuster, News and Public Affairs Specialist,
334-844-5686.]
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