Biofilms on food preparation surfaces

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Introduction

Scanning electron microscopy photomicrograph of a 6 old B. cereus biofilm formed on a stainless steel surface. x 6330 magnification; bar = 5 micron.[1]

Biofilms are a consortium of microorganisms and extracellular substances in association with a solid surface in contact with liquid. It is nature of microorganisms to attach to wet surface, and form slimy layer composed of extracellular polymeric substances (EPS) to protect themselves from grazers and harsh environment. Biofilms can be beneficial or detrimental to the environment on which they form. For example, stream biofilm is capable of recycling organic matter. On the other hand, biofilms forming on food-contact surfaces can lead to hygienic problems and economical losses due to food spoilage. Food-contact surfaces can be a great habitat for food-borne pathogens because food preparation surfaces are usually in contact with organic matter such as milk which is a good source of nutrients for microorganisms, with inorganic debris, with other microorganisms. Once bacteria irreversibly attach to the surface, they produce EPS, which helps bind cells together, to the surface, and to other particulate materials. Cells also communicate between themselves to initiate antibiotic biosynthesis, and extracellular enzyme biosynthesis.

Physical environment

Physical properties of the environment are essential for microorganism attachment to the substratum, biofilm formation ,and microbial processes. For example, food conditioning surfaces may promote the attachment of bacteria. The pH and temperature also affect microbial metabolism processes. Some of the physical conditions are explained below.

Conditioning of a Surface

Biofilm formation can occur on any submerged surfaces in any environment with the present of bacteria. On food preparation surfaces, bacteria, inorganic and organic materials get adsorb on the surface in minutes of substratum immersion into liquids leading to conditioning surfaces. In food industry, this conditioning film may be proteins from milk or meat. Protein from milk was studied to adsorb to numbers of food-contacting surfaces such as Teflon, stainless steel, and aluminosilicate [3]. The conditioning can alter physio-chemical properties of the surface, surface charge, surface free energy, surface hydrophobicity, which further results in bacterial attachment on the surface. [4].

Surface Charge and Hydrophobicity

Surface charge and hydrophobicity of both bacterial cells and a conditioning surface play an important role in microbial attachment on the surface. These two factors have an impact on the length of time cells are associated with the substratrum. Surface charge results in electrostatic interaction between 2 surfaces. Moreover, cell surface hydrophobicity is also important in adhesion because hydrophobic interaction tends to increase with increasing non-polar property of each surface.

Surface Topography

The relationship between surface roughness and the attachment and growth of bacteria may vary. It was shown that two strains of Yersinia have a strong correlation between the roughness amplitude of the substratrum and adhesion. On the other hand, another showed that little correlation was found on attachment of streptococci to stainless steel.

pH and Temperature

The pH and temperature of a contact surface govern many physical and biological processes of bacterial cells. It was studied that the maximum adhesion of Pseudomonas fragi to stainless steel surfaces was at the pH range of 7 to 8, which was also optimum for cell metabolism. Another study showed that Yersinia enterocolitica attached to stainless steel surfaces better at 21 °C than at 35 °C or 10 °C.

Oxygen Availability and Moisture

The oxygen gradient in a schematic biofilm.[2]

The structure of biofilms has a porous structure with a number of capillary water channel within which water and nutrients are transported through. It is believed that these capillaries are responsible for oxygen transport to the inner areas of biofilms. Unfortunately, due to oxygen limited diffusion ability and oxygen consumption, the inner areas encounter low oxygen concentration or anaerobic condition. This phenomenon explains why aerobic and anaerobic bacteria can live together in biofilms.

Stainless Steel as a Food Source Contact Surface

Stainless steel is the most common food contact surface used in the food industry. Stainless steel is suitable for the food industry because of the stability of physical and chemical properties at a various processing temperature. It is highly resistant to corrosion and easy to clean. However, if taking a look at microscopic level of stainless steel surface, it is amazing that stainless steel is composed of cracks and crevices. These structures are different from macroscopic appearance. Such topography allows bacteria and organic substances from food to attach. Studies have shown the attachment of food-borne pathogens and spoiled microorganisms to stainless steel.

Biofilm formation

Processing governing biofilm formation.[1]


Biofilm formation includes a sequence of steps as shown in a picture.

Biological interactions

Are there important biological interactions that are important in this environment? Do these interactions influence microbial populations and their activities? How do these interactions influence other organisms? Describe biological interactions that might take place in this environment, using as many sections/subsections as you require. Look at other topics available in MicrobeWiki. Create links where relevant.

Biofilm Ecosystem Development

Coaggregation and Aggregation

Subsection 1a

Subsection 1b

Conjugation

Subsection 1a

Subsection 1b

Intercellular Communication within Biofilm Communities

Quorum Sensing

Cell-to-Cell Communication

Microbial processes

What microbial processes define this environment? Describe microbial processes that are important in this habitat, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.

Extrcellular Polymeric Substances (EPS)

Key Microorganisms

What kind of microbes do we typically find in this environment? Or associated with important processes in this environment? Describe key groups of microbes that we find in this environment, and any special adaptations they may have evolved to survive in this environment. Add sections/subsections as needed. Look at other microbe listings in MicrobeWiki. Are some of the groups of microbes from your environment already described? Create links to those pages. Specific microbial populations will be included in the next section.

Listeria monocytogenes, Salmonella spp., Staphylococcus spp., Escherichia coli O157:H7

Listeria monocytogenes

important foodborne pathogen-listeriosis outbreak in Canada psychophilic bacteria- grow in refrigerated ready-to-eat food that may be contaminated during processing and packaging.

Pseudomonas spp.

the most important bacteria causing spoilage of conventionally pasteurize liquid milk products: 2 routes 1)raw milk- enzyme 2)post pasteurization milk

Examples of organisms within the group

List examples of specific microbes that represent key groups or are associated with important processes found in this environment. Link to other MicrobeWiki pages where possible.

Current Research

Approach for Biofilm Mitigation- biofilm prevention

Green Strategy for Biofilms Control

Cleaning and Removal of Biofilm

Microscopic Examination of Biofilms

Attachment of Microorganisms on Food Contacting Surfaces

Enter summaries of recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Angela Kent at the University of Illinois at Urbana-Champaign.