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Bacterial Biofilms Less Likely on Electropolished Steel

Bacteria on surface--2,500x
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 washing.

Bacteria on stainless steel surface--500x
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.

Resistant bacteria on surface--1,500x
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 quality control."

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.

Bacteria on electropolished steel--700x
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 equipment regularly."

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."

Bacteria on surface--10,000x
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) 344-2781.

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. Click here to see this issue's table of contents.


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