Bacterial Biofilms Less Likely
on Electropolished Steel
As bacteria accumulate on surfaces, they
exude a complex matrix of fibrils that
connect cells, and many bacteria align side
to side. Magnified about 2,500x.
When the news came out that stainless steel can harbor
bacterial biofilms, a Dallas, Georgia, company decided to test its metal
against other materials. The results were good news for anyone wanting to
reduce bacterial cross-contamination in poultry.
Cross-contamination occurs as poultry is processed and bacteria from
carcasses attach to wet steel surfaces on processing equipment. When the
bacteria accumulate, they develop an increasingly complex matrix by attaching
to each other and forming a bacterial film that stubbornly resists normal
Most of the surfaces in a food processing plant
are made of stainless steel that is susceptible
to bacterial attachment, as seen here. Magnified about 500x.
Wayne Austin is vice president of Simmons Engineering
Company. The firm specializes in poultry processing machines. Austin knew that
Agricultural Research Service's Judy W.
Arnold was testing various kinds of steel for resistance to bacterial
attachment. So he asked her to include his company's electropolished steel as
part of her research protocol.
Test results showed that the process developed by Simmons to give their
machine steel a shiny, chromelike appearance also kept bacteria at bay.
Arnold, a microbiologist in the ARS Poultry Processing and Meat Quality
Research Unit at Athens, Georgia, found surface finishing treatments such as
polishing, sandblasting, and grinding all reduced buildup of bacterial
biofilms. But eletropolishing seemed to work the best.
The bacterial composite forms a biofilm that
is resistant to cleaners and sanitizers. Magnified about 1,500x.
Electropolishing involves placing steel in an acid bath,
then running an electric current through the solution. Arnold has a theory
about why this prevents bacterial biofilms: The process may change the
electrical charge on the metal. Bacteria are negatively charged, and the charge
on a given surface can affect how well they attach to it.
Arnold's findings are important. One reason is that the federal HACCP
(Hazard Analysis Critical Control Points) inspection policy requires all meat
producers to identify potential contamination areas and take preventive
measures. The findings are especially important to the poultry industry because
of the fast-paced production.
"Some of our evisceration machines can process 90 to 140 birds a
minute," says Austin.
"If eletropolishing can prevent the cross-contamination of bacteria
between birds and the buildup of bacteria over time--that's an important
But it's not just equipment manufacturers who worry about
cross-contamination. ARS sponsored a special forum on poultry research at which
Arnold presented findings that caught the attention of Michael Robach, vice
president of food safety at Continental Grain.
Stainless steel that has been electropolished
shows significantly fewer bacterial cells and beginning biofilm formations.
Magnified about 700x.
Headquartered in Gainesville, Georgia, Continental Grain is
the sixth largest broiler producer in the United States. The company
distributes 1.2 billion pounds of ready-to-cook meat and 100 million pounds of
ready-to-eat chicken each year.
Robach says he plans to use Arnold's slides of bacterial biofilms on steel
to make a point when training plant managers on sanitation and safety.
"We want to show them that just because a steel surface looks clean
doesn't mean it's bacteria-free," he says. "Our safety protocol
includes using chlorine dioxide to disinfect, and we replace our processing
Arnold says the surface treatments, scouring and others, could be more
effective than some cleansers and may also reduce the amount of chemicals
required to keep plants sanitary.
"I think industry executives get tired of people throwing chemicals at
them as the only solution to Salmonella," says Arnold. "What I
have to offer will be an effective part of contamination prevention--perhaps
with reduced environmental impact."
When bacteria attach to a surface, they
produce extracellular polymers that
anchor the cells and provide a favorable
site for attachment and growth of more
bacteria, other microbes, and debris.
Magnified about 10,000x.
Arnold says she now plans to explore how and where various
bacterial species develop biofilms in processing plants. She will also explore
new chemical pre-treatments to prevent biofilms.--By
Jill Lee, Agricultural Research Service
Information Staff, 6303 Ivy Lane, Greenbelt, Maryland 20770, phone (301)
Judy W. Arnold is in the USDA-ARS,
Poultry Processing and Meat
Quality Research Unit, Russell Agricultural Research Center, 950 College
Station Rd., Athens, GA 30604; phone (706) 546-3515, fax (706) 546-3548.
"Bacterial Biofilms Less Likely on Electropolished Steel" was
published in the February 1998 issue of Agricultural Research magazine.
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