Food Safety Magazine, June/July 2012

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SANITATION “...a challenge that food processors and their sanitation teams face is the formation of biofilms on food equipment surfaces.” to normal sanitation procedures and can result in other detrimental process effects. Even when a food surface appears to be clean, the presence of biofilms is a potential hazard that must be eliminated and prevented from reoccurring. Before this can be done, it is important to understand what a biofilm is and how it is formed. Biofilms begin with a bacterial adhesion, referred to as a conditioning layer, of organic (protein) or inorganic matter forming on an otherwise visually clean food contact surface (Figure 1). The accumulation of organic and inorganic material on processing surfaces creates an environment where bacteria can adhere. Live, damaged or dead cells can attach themselves to the conditioning layer and begin colonization. The conditioning layer starts as a thin, resistant layer of microorganisms, any combination of spoilage and pathogenic bacteria that form on and coat the conditioning layer. As the layers of bacteria attach to the surface and each other, they trap debris and nutrients, and the biofilm begins to take shape. Bacterial appendages (e.g., fimbriae, pili and flagella) may also facilitate the attachment of other cells or materials to form the colony. For example, L. monocytogenes likely attaches to surfaces by producing attachment fibrils. During attachment, cells in the forming colony work together in a coordinated and cooperative fashion, including channeling nutrients to the film and removing waste products. As the colony continues to attach, there is production of extracellular polysaccharides and changes in cell morphology. Extracellular polysaccharide formation aids adhesion of the cells in the film and protects the bacterial layer against cleaners and sanitizers. The polysaccharide will also trap other cells and debris. Dr. Virginia Deibel states that the extracellular polysaccharide material forms a bridge between bacteria and the conditioning layer with a combination of electrostatic and covalent bonds. 2 Development and growth, without removal intervention, results in the film becoming irreversibly attached to a substratum, interface or to each other, embedded in a matrix of extracellular substance that they have produced. Mature film reaches an equilibrium that delivers oxygen, food and nutrients while carrying away fermentation products and sloughed cells. The outermost slime layer of film serves as a snare that traps additional contaminants and acts as a protectant, sealing the bacteria within so that the protected bacteria can be up to 100 times more resistant to sanitizer. As an example, L. monocytogenes in biofilms is more resistant to sanitizers than those not in films. Inorganic and organic material flowing over the biofilm provides nutrients to the colony. Inside the biofilm, damaged or small cells may have the time to repair themselves and reproduce. The film is irreversible and now requires a special cleaning protocol for removal. Biofilms form at a slow but steady rate and, much like tooth tartar, become harder to remove over time. They can form on almost any surface but are most likely to form on rough, penetrable surfaces, such as those that are scratched, pitted, corroded or cracked. 3 They can attach to all types of surfaces in food plants, from stainless steel, especially on abraded or scratched surfaces, to polypropylene. Biofilms may form in hard-to-reach areas, such as the undersides of conveyor belts and seals. For this reason, it is necessary to regularly inspect and change equipment parts such as gaskets, O-rings and piping. Where possible, food plants should identify and eliminate areas that cannot be thoroughly cleaned through sanitary design of equipment. Extended production runs with minimal cleanup in between also increase the chances and frequency of films developing due to increased organic material contact time, opportunity for organisms to multiply and formation of the conditioning layer. These longer runs also cut into valuable sanitation time and reduce the ability of sanitarians to do their job as designed, causing them to rush or take shortcuts. Additional factors that contribute to biofilm formation include the lack of stringent cleaning regimes, pH extremes and high contactsurface temperatures that denature proteins, facilitating the formation of a conditioning layer, a low fluid flow rate and nutrient availability. Challenges Associated with Biofilms There are several problems associated with biofilms, not the least of which is product contamination. Product contamination occurs from sloughing bacteria that are shed periodically by the film and can reattach on equipment somewhere else in the product flow or can make their way into food product. If these are spoilage organisms, product shelf life may be reduced, and consumer purchases, especially repeat purchases, may decline. However, if they are pathogens, the product may be considered adulterated and subject to recall, or it may be responsible for a foodborne illness outbreak. Any company that has been involved in a recall or whose product has been associated with an illness can attest to the fact that biofilms are damaging to the business and extremely expensive. Organisms within the film are also more heat resistant, so sloughed cells from films that form before cooking may not be destroyed as readily by the lethality process. Just as dental plaque damages teeth through the production of acids as a byproduct of bacterial metabolism, biofilm formation comes with associated problems, such as accelerated deterioration of equipment through corrosion from cellular byproducts. There may also be a reduction in the efficacy of heat transfer and impairment of detection devices as the film disrupts transmission. As previously indicated, attached cells can develop increased resistance to cleaning chemicals and sanitizers possibly due to protection provided by the polysaccharide layer. The reduction in effectiveness of chemicals may be the 22 F o o d S a f e t y M a g a z i n e
SANITATION result of cells layering and the reduction of exposed surfaces on which the chemicals make contact. As an example, cells of L. monocytogenes in biofilms have been found to be more resistant to sanitizers than nonattached cells. Evidence of Biofilm There are several means of determining that a biofilm has begun to form on a food contact surface. Detection may be via the use of several senses. Visual signs include a “rainbow” appearance on stainless steel, and tactile senses will detect a slimy feel on otherwise clean-appearing equipment surface. Although sour or off-odors may not indicate the presence of biofilms, they may indicate that a piece of equipment is not being cleaned thoroughly and that there is a potential for biofilm formation. From an analytical standpoint, another indicator of biofilms is a sporadic spike in environmental test results due to bacterial sloughing. These indications may be found through generic microbiological tests such as aerobic plate count or through environmental pathogen testing for plants conducting Listeria swabs. An increase in the bacterial counts or positive findings may indicate the formation of a biofilm and bacterial sloughing. Unfortunately, if they are not detected soon enough, the result may be sporadic product microfailures or decreased product shelf life. However, if you are already at a point where product has begun to fail shelf life or demonstrate higher than normal bacterial counts, it would be wise to consider the possibility of biofilm formation and apply control measures to eliminate it. Adenosine triphosphate (ATP) bioluminescence devices can be used to detect the presence of organic materials; unfortunately, ATP may not detect the presence of mature biofilms. The reason for this is that embedded cells do not move as much due to nutrient availability and use less energy, thus producing less ATP. Therefore, the device may deliver a “Pass” reading on a surface where there is a biofilm. Biofilm Removal There should be no good reason for the films to build if there is good sanitary equipment design and regular and thorough cleaning to remove surface soil and subsurface film. <strong>Food</strong> manufacturing equipment poses many sanitary design challenges. Equipment has hollow rollers and tubing, welds, joints and scrapers that make cleaning difficult. Once biofilms have established themselves on a surface, they are harder to remove as they develop over time and require more aggressive action to eliminate. Fortunately, the original biofilm attachment is weak and easy to remove through proper sanitation procedures. Therefore, the film soil must be removed, and the most effective method of cleaning is a standard process, described below: Dry clean. This is done to remove as much visible soil or product material as possible. This may involve scraping, brushing, vacuuming, sweeping or shoveling to (continued on page 76) Biofilms Have a New Foil… STERILEX ® PerQuat Technology “Results showed that the formulation was 100 percent effective, providing total kill and more than 90 percent biofilm removal. This disinfectant is more effective than currently used disinfectants in reducing L. monocytogenes biofilm growth.” —Judy Arnold USDA Microbiologist ENHANCE YOUR SANITATION PROGRAM INNOVATIVE SOLUTIONS FOR MICROBIAL CONTROL For more information, call 800.511.1659 or email sales@sterilex.com J u SterilexPerQuatAd.indd n e • J u l y 2 0 1 21 5/9/12 4:50 PM 23
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Page 6 and 7: Editor’s Letter It’s All About
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Page 10 and 11: News Bites 2012 Food Safety Summit
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Food Safety Magazine, June/July 2012

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