Biofilms in the Food and Beverage Industries

P M Fratamico, B A Annous, N W Guenther

• Publisher: Woodhead Publishing
• Year: 2009
• Print ISBN:
  9781845694777
• eBook ISBN:
  9781845697167
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

When bacteria attach to and colonise the surfaces of food processing equipment and foods products themselves, there is a risk that biofilms may form. Human pathogens in biofilms can be harder to remove than free microorganisms and may therefore pose a more significant food safety risk. Biofilms in the food and beverage industries reviews the formation of biofilms in these sectors and best practices for their control.The first part of the book considers fundamental aspects such as molecular mechanisms of biofilm formation by food-associated bacteria and methods for biofilm imaging, quantification and monitoring. Part two then reviews biofilm formation by different microorganisms. Chapters in Part three focus on significant issues related to biofilm prevention and removal. Contributions on biofilms in particular food industry sectors, such as dairy and red meat processing and fresh produce, complete the collection.With its distinguished editors and international team of contributors, Biofilms in the food and beverage industries is a highly beneficial reference for microbiologists and those in industry responsible for food safety. - Considers fundamental aspects concerning the ecology and characteristics of biofilms and considers methods for their detection - Examines biofilm formation by different micro-organisms such as samonella and food spoilage - Discusses specific issues related to biofilm prevention and removal, such as cleaning and sanitation of food contact surfaces and food processing equipment

Part I

Biofilms in the food and beverage industries

1

Biofilms in the food and beverage industries: an introduction

E. Cloete Stellenbosch University, South Africa

I. Molobela; A. Van Der Merwe; M. Richards University of Pretoria, South Africa

Abstract

Microbes, (bacteria, fungi, yeasts, moulds, viruses, etc.) are primarily found in two forms, either floating freely in water (planktonic), or attached to a surface (sessile) where they congregate in large numbers to form a film or slime layer known as a biofilm. Although planktonic microbes have been studied for many decades, it is only in the past two decades that industry has begun to understand and appreciate the complexity of a biofilm as a living organism and the huge problems biofilm formation causes in industry. It is now acknowledged that biofilms have huge cost implications to industry and can negatively affect a company’s profitability. Biofilm is extremely difficult to remove and control. It is common knowledge that many chemical biocides are ineffective against biofilm and, at best, merely control planktonic microbes – leaving the biofilm intact to continue to recontaminate, corrode and to build resistance against antimicrobial compounds. The added danger then is when a particularly undesired pathogen (e.g., E. coli in food processing, Legionella in cooling towers, Pseudomonas in poultry rearing) enters a system and becomes attached to the biofilm, it becomes extremely difficult to remove and control, causing enormous problems that often result in production and plant shut-downs – costing companies millions in lost revenue.

Key words

biofilms

extracellular polymers

biocides

bacteria

resistance

1.1 Introduction

A biofilm can be defined as the sessile community of microbes characterized by cells that are irreversibly associated with a surface, embedded in a matrix of extracellular polymeric substances (EPS), and display an altered phenotype with respect to gene expression, protein production and growth. Biofilms can form on a wide variety of surfaces and the biofilm thickness varies from a single cell layer to a thick community of cells embedded in EPS. Materials like corrosion particles, clay, slit and mineral crystals, depending on the environment in which the biofilm has formed, may also be found in the biofilm matrix (Donlan, 2002).

Microorganisms in biofilms display some particular features that are not shared with the same microorganisms in suspended form. In biofilms, the cells are embedded in a polymer matrix of their own origin that mainly consists of polysaccharides and proteins. Biofilms contain mixed populations of bacteria, fungi, protozoa and if conditions allow, they can host even higher organisms in the food chain such as nematodes and larvae.

Biofilms represent a very complex form of microbial life that is mainly characterized by a high degree of interaction between different types of organisms and by a more or less immobilized form of life. This allows the formation of stable aggregates in which synergistic effects can develop. In biofilms, the cells can tolerate much higher concentrations of biocides in suspension (Flemming, 1998). Another characteristic of biofims is their heterogeneity; for example, aerobic microorganisms in aerobic system consume oxygen resulting in an anaerobic zone within the biofilm (Flemming, 1998). This process provides habitats for anaerobes that could not proliferate under aerobic conditions.

A biofilm is mainly composed of water (80–90%), extracellular polymer substances (EPS) that contribute 85–98% of the organic matter, the microorganisms, entrapped organic and inorganic particles, substances sorbed to EPS, cells or particles and substances dissolved in the interstitial water (Flemming, 1998). Microorganisms are characterized as freely suspended cells (planktonic) and are described on the basis of their growth characterizations in nutritionally rich culture media.

In a natural aquatic ecosystem, surface associated microorganisms consist of different organisms in suspension. The ability for bacteria to colonize surfaces is advantageous from an ecological point because specialized bacteria are preferentially targeted to specific locations, encouraging symbiotic relationships. Examples of these relationships are taking place in nature, e.g. prokaryotic diazotrophs that colonize the roots of the legumes (Pearce et al., 1995) and the diverse residential microbial flora inhabiting the digestive tract of ruminants that promotes the degradation and recycling of insoluble materials (Cheng et al., 1995).

It is advantageous for bacteria to form biofilms since this mode of growth provides the bacteria with elevated levels of protection (Allison et al., 2000; Mara and Horan, 2003) against fluctuating environmental conditions (pH, nutrients, oxygen and shear forces), disinfectants, antibiotics and host immune responses (Jefferson, 2004). All bacteria within biofilms live together and depend on other microorganisms for energy, carbon and other nutrients. Thus, most of the bacteria live in micro ecosystems filled with hundreds of other microorganisms and form biofilms. When in this form, bacteria can be up to a 1000 times more resistant to antimicrobials than their planktonic counterparts (Mah and O’Toole, 2001; Drenkard, 2003). Biofilm bacteria attach and reside in environments that are favorable and, when exposed to unfavorable conditions, cells can detach and move to new locations.

The metabolism of the cells in a biofilm is reduced due to its heterogeneous nature. Heterogeneity arises due to different diffusion rates of nutrients and oxygen within the biofilm, creating oxygen, substrate and pH gradients. This in turn allows bacteria at different locations in the same biofilm to carry out different metabolic tasks and produce different gene products (Jefferson, 2004). Kreft (2004) points out another advantage of communal growth by confirming altruistic behavior in biofilms. Altruism can be defined as the unselfish behavior of one group in order to enhance the fitness of the entire group. An example of altruistic behavior is where cells exhibit a low growth rate in order to decrease the use of nutrient sources and increase the growth yield and strength of the group (Kreft, 2004).

Gene transfer between biofilm bacteria is believed to be favored due to the extended contact time of bacteria within biofilms and the steadiness of cells on the surface (Allison et al., 2000). Gene transfer increases the genetic diversity of bacteria and supplies the bacteria with antibiotic resistance genes and other genes of interest (Jefferson, 2004). Ghigo (2001) demonstrated the role of conjugative plasmids in the development of biofilms. These plasmids encode pilli that assist in the attachment of E. coli and other Gram-negative cells to each other and to surfaces and therefore lead to the conversion of planktonic cells to biofilm state. In this manner the plasmids ensure their spread to other bacterial cells (Ghigo, 2001).

The switch from planktonic to a biofilm mode of growth is an intricate process, which occurs in response to changes in environmental conditions (O’Toole et al., 2000). For this switch to take place certain genes are up- or down-regulated (Kuchma and O’Toole, 2000). Biofilm bacteria differ from their planktonic counterparts in genes they express (Prigent-Combaret et al., 1999; Becker et al., 2001; Sauer and Camper, 2001; Whiteley et al., 2001; Oosthuizen et al., 2002; Sauer et al., 2002; Schembri et al., 2003; Beloin et al., 2004; Beenken et al., 2004; Ren et al., 2004); the rate at which the cells grow (Huang et al., 1995; Cloete, 2003a,b) and their resistance to biocides and antibiotics (Anderl et al., 2000; Brooun et al., 2000; Norwood and Gilmour, 2000; Ryu and Beuchat, 2005).

Biofilms can be formed on all types of surfaces in most ecosystems where nutrients are ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Preface
• Part I: Biofilms in the food and beverage industries
• Part II: Microorganisms and their metabolites in biofilms
• Part III: Biofilm prevention, inactivation and removal
• Part IV: Biofilms in particular food industry sectors
• Part V: Appendix
• Index