Biofilms — what are they?

Biofilms are clusters of microorganisms attached to surfaces embedded in a self-produced matrix. While there are beneficial biofilms within the digestive tracts of warm-blooded mammals like cows (and humans) that provide milk, biofilm colonization of the plant environment regularly poses food safety and quality challenges for food and dairy processors. 

While we may collect samples and use a laboratory to selectively culture for the presence of one type of organism for surveillance of our facility environments, biofilms rarely exist as a single species. Rather, biofilms are usually a multi-species community of organisms in a symbiotic relationship benefitting from each other. Bacteria, yeasts, and molds often form this thick, complex surface-attached community with water channels carrying dissolved oxygen and nutrients throughout the film.

How do biofilms develop in our food and dairy operations?

Biofilm growth conditions include incomplete removal of food soils in or on equipment, or within the dairy plant itself. Ineffective sanitation may be caused by poor sanitary design or ineffective cleaning practices. Beyond pits, folds, cracks and inclusions, interfaces, and non-self-draining equipment in the environment, hydrophilic surfaces such as stainless steel also can harbor biofilm.

Biofilms are cemented together by exopolymeric substances (EPS) containing polysaccharides that are resistant to removal. If soil is present on unclean surfaces for as little as 72 hours, a biofilm may develop; and if not removed, can reach structural maturity in as little as 10 days, becoming very difficult to penetrate and remove.   

Biofilms present food safety/quality risk and decrease operational efficiency

Pathogenic bacteria such as Listeria monocytogenes, Enteropathogenic E. coli., and Salmonella are often found in mixed culture biofilms. These deadly organisms cause a large number of foodborne illness and deaths annually. 

Besides pathogenic disease, biofilms are often implicated in spoilage incidents and shortened shelf life of dairy products due to the shedding of spoilage bacteria from the films into milk, cheese, and yogurt. 

Biofilms may also create inefficiency or degradation of our assets in plant operations from accumulations in heat exchangers and corrosion of plant utilities 

Tips to prevent biofilm development and inhabitation in dairy operations

The microorganisms that form biofilms within dairy plants do not spontaneously generate to cause biofilms in operations. They do not enter our plants through their own mobility; they are introduced and move around plants via vectors. Potential vectors include people (footways), raw materials, finished product distribution (wheelways), plant air makeup, and gradient (pressured from high care out to low care and exhausted). An effective hygienic zoning plan is crucial to control the vectors that bring microorganisms into the plant and methodically distribute biofilms into low care, medium care, and high-care environments.

Sanitation practices key to keep biofilm development at bay

General plant control: Warehousing and storage areas should remain dry as much as possible. Zone dedicated floor scrubbers may be used in the storage areas. The last application with the floor scrubber should be a residual sanitizer such as a quaternary ammonium compound (QAC) solution at environmental strength.

Limit the amount of water used in the trafficways of the wet cleaned environment. Water used in walkways to include processing, liquid dairy ingredient areas such as “silo alleys” and wet packaging areas must be controlled. Avoid using water in the environment without a final application of environmental strength sanitizer solution. Operations that occasionally need water for interdictive cleaning due to spills or packaging jams should use a prepared sanitizer solution from a central sanitize system for clean up during processing, filling, and closing.  Water hoses should be removed from hose bibbs at production startup. 

Ensure plant workers practice an effective drain cleaning program with careful segregation and control of tools and containers. Surveil for pathogens with a robust EMP mitigation program. If a  pathogen in a drain is recovered, vector upstream 3 dimensionally inspecting ceiling, utilities, equipment framework in addition to floor areas for the source. While drains represent a collection point, they generally represent less risk than the upstream source of the pathogens.  

Wherever practical, modify existing wet or foam applications of sanitizer for walkways and wheelways to non-aqueous or the newer powdered technologies to include the powdered peroxide-based formulas. 

Wet cleaned processing and packaging areas: Areas where processing is performed and where water is used for cleaning usually present the most risk for biofilm development.  A thoughtful Sanitation Standard Operating Procedures (SSOP) should be developed to ensure complete removal of soils from these environments calling out hard-to-access areas for cleaning and verification. These environmental areas (in addition to equipment verification) must also be included in the flashlight and stainless-steel mirror inspection to verify sanitation effectiveness. An application of sanitizer should follow the post-rinse after cleaning. Foaming peracid sanitizers work very well to control outgrowth. A foaming Quaternary Ammonium Compound (QAC), a chemical used to kill bacteria, viruses, and mold, also is effective if it is acceptable to have QAC in your effluent.

Wet cleaned processing, filling, and closing equipment: Wet cleaned equipment should have the CIP or manual cleaning comply with an accompanying validated SSOP. If your SSOP is not validated, it will place more reliance on your verification step until you can validate your SSOP’s. 

If the plant’s equipment has a validated SSOP, there are established critical factors to verify to flow rate, chemical concentration, time, and temperature. Using these critical factors each time cleaning commences will ensure success. Verifications to ensure there is an absence of soil with a flashlight may require the beam to be held at an angle on some surfaces to visually verify clean. A stainless-steel mirror is an excellent accompaniment to the flashlight to look under framework, motors, pumps, homogenizers, HPP’s and other equipment.

Residues left under equipment and framework are a common reservoir for biofilms in a dairy plant. 

These should be removed from each sanitation cycle to prevent a difficult, hardened biofilm and general biofilm issues that may spread around the facility. 

Powdered high-care packaging areas for RTE, infant formula, neutropenic foods:  Whenever possible and as the infrastructure permits, move the packaging areas from wet cleaning to dry cleaning. This will significantly reduce pathogen recoveries.   (See Dairy Foods magazine December 2022 – “Dry Cleaning for your Operations – Advantages and Challenges” for more information on hygienic design and practice for dry cleaning).

Regimen to inactivate and remove developed biofilms

Literature suggests that biofilms allowed to establish themselves for a “period of time” may become “irreversible.” However, I believe irreversibility of the biofilm attached to a surface from the exopolysaccharides is subjective. This tends to be variable depending on the surface roughness, drainability, and hygroscopicity of the area involved. The condition of the plastics and elastomers also is an important factor since rubbers, plastics, and elastomers that are involved in recoveries of an undesirable organism should be replaced. All associated surfaces should be brought up to a high sanitary level to start the restoration of a positive finding. 

Remember, though, that environmental monitoring should follow the restorative clean to confirm the biofilm has been inactivated. As this column has stressed, prevention of biofilms in the dairy plant is key to the success of dairy operations. Once biofilms are established, they can be difficult to control.