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Curtailing Campylobacter
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Technician Anna Bates and
microbiologist Robert Mandrell
examine Campylobacter on
chicken skin with laser scanning
confocal microscopy.
(K8243-4)
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If a microbe is able to cling to the
surface of a food, it may use that site as the launching point for a successful
invasion. But what if the natural mechanisms that enable microbes to establish
these beachheads could somehow be undermined?
That's the goal of new investigations by ARS research microbiologist Robert E.
Mandrell and colleagues. They are with the ARS Food Safety and Health Research
Unit at the Western Regional Research Center, Albany, California.
Scientists have known for decades that Campylobacter jejuni, a
food-poisoning microbe, sticks to poultry skin. "But," Mandrell
admits, "we don't know the details. We don't know what genes are activated
when the microbe first comes in contact with the skin. We suspect that specific
molecules in the skin act as receptors that the pathogen can bind to, but we
don't know that for certain. Nor do we know how many different kinds of
receptor molecules are involved," he says. "Most important, we don't
yet know what we can do to make the receptors fail." |
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Microscopic fluorescent green
Campylobacter cells on
chicken skin.
(K9516-1)
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Major Cause of Food Poisoning
Campylobacter causes about 2 million human illnesses, 10,000
hospitalizations, and 100 deaths a year, according to estimates from the
Centers for Disease Control and Prevention.
Preliminary experiments at the Albany laboratory have Campylobacter binds
to and have shown how quickly the connection happens.
For these tests, Mandrell and co-researchers exposed extracts of ground-up
chicken skin to various strains of C. jejuni, the Campylobacter
species of most concern. Eight of the nine C. jejuni strains bound to a
fat-containing compound, or phospholipid, known as sphingomyelin. Fewer strains
bound to other phospholipids, such as phosphatidylcholine. In addition, more
Campylobacter cells bound to sphingomyelin than did cells of another
foodborne pathogen, Salmonella. |
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Robert Mandrell examines
colonies of Campylobacter
jejuni.
(K8243-15)
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Affinity for a Protein
In another test, the researchers examined a mixture of proteins—found in
chicken skin and known as proteoglycans. All 12 Campylobacter strains
examined bound to proteoglycans. And, reports Mandrell, the microbes bound more
snugly to a proteoglycans mixture than to a purified sample of one specific
proteoglycan, collagen.
Campylobacter bound to proteoglycans within 2 minutes after being
exposed to the mixture, Mandrell says. Within about 20 minutes, the pathogen
formed large colonies.
Mandrell did the work with Anna H. Bates, David L. Brandon, Amy O. Charkowski,
Gary A. McDonald, and William Miller of the Albany team.
Earlier studies, done elsewhere, had already shown that Campylobacter
can bind to proteoglycans. But the Albany experiments were apparently the first
to use proteoglycans extracted from actual chicken skin. The team's research
has revealed differences in the affinity of various Campylobacter
strains to the natural mixture of proteoglycans as well as differences in how
fast the binding takes place.
Other scientists have speculated that proteins or fats in meats may act as
receptors, helping Campylobacter to stick. The Albany investigations
suggest that proteoglycans and phospholipids such as sphingomyelin may play
that role in poultry.
Markers Trace Microbe's Invasion
To track Campylobacter cells on chicken skin, research microbiologist
William Miller uses a fluorescence-imparting gene from the Pacific jellyfish,
Aequorea victoria. He paired that gene with a portion of a
Campylobacter gene called a promoter, to turn on the jellyfish gene.
Miller then moved the pair into Campylobacter cells.
The transformed Campylobacter cells continuously glow vivid yellow,
brilliant green, or bright blue-green—colors that are easy to see under
ultraviolet light in the lab.
Having an array of different colors enables the scientists to spy on the
progress of multiple strains or multiple species of Campylobacter at
once. That's important because more than one kind of Campylobacter might
be living in or on a chicken at one time.
In fact, this color-coding option has already helped the team. Using it, they
found new evidence that different strains of Campylobacter—each
sporting its own color in the experiments—can coexist as an aggregate.
"Without this distinguishing coloration," says Miller, "cells
isolated from these aggregates could easily be mistaken for a single, pure
strain. It's important to know whether a colony is made up of more than one
strain," he points out, "because each strain may behave somewhat
differently. To zap each strain, you might need to use more than one
technique."
Miller collaborated in this work with Bates, Mandrell, Maria T. Brandl, and
Sharon T. Horn at Albany, and with Marian R. Wachtel, formerly at Albany and
now with ARS at Beltsville, Maryland.
More Promoters Observed
In other investigations, Miller and colleagues are linking the jellyfish gene
to an assortment of several hundred other Campylobacter promoters. The
intent: to pinpoint Campylobacter genes that are key in helping the
microbe stick to skin and survive on or inside poultry. Unlike the promoters
that cause Campylobacter cells to glow nonstop, this second series of
promoters is configured to turn on the jellyfish gene only when the promoters
receive signals from Campylobacter cells.
"Let's say Campylobacter cells with a particular promoter inside
begin to glow as they start attaching to chicken skin," says Miller.
"That probably means this Campylobacter promoter is normally
configured with a Campylobacter gene that's in some way involved with
helping the bacteria adhere. Once we've identified these critical genes, we may
be able to block their activity."
Scientists have used fluorescence-imparting genes from the Pacific jellyfish
since at least 1994. Miller's work has shown that fluorescing
Campylobacter cells are faster and easier to use than some other
options.—By Marcia Wood,
Agricultural Research Service Information Staff.
This research is part of Food Safety and Health, an ARS National Program
(#108) described on the World Wide Web at http://www.nps.ars.usda.gov. To reach
scientists mentioned in this article, contact
Marcia Wood, phone (510) 559-6070,
fax (510) 559-5882. |
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"Curtailing Campylobacter" was
published in the July
2001 issue of Agricultural Research magazine.
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