BIOFILM AND THE EPS

WHAT IS A BIOFILM?

While approximately 10% of bacteria are free-floating (planktonic), the remaining 90% naturally form colonies called biofilms.5 A biofilm is a living, dynamic, polymicrobial community of organisms attached to a surface, or to one another, encased within a self-secreted matrix of extracellular polymeric substance (EPS).6,7 The EPS accounts for over 80% of the volume of the biofilm and the biological environment is generally composed of polysaccharides, proteins, glycolipids, blood products, cellular debris, extracellular enzymes and DNA, as well as other components.6

Biofilms can form in less than one hour8 as a defence mechanism to prevent bacterial eradication. As opposed to planktonic bacteria, biofilms are powerful communities that function as a single entity with behaviours and defences that can produce chronic or recurrent infections.9 A biofilm can consist of several bacterial or fungal species.10

According to the US National Institute of Health, biofilms account for over 80% of microbial infections in the human body.1

HOW DOES A BIOFILM FORM?

The formation of a biofilm is divided into six stages:

  1. Formation of a conditioning film containing proteins, sugars and blood products that is evident on any existing or newly formed virgin surface (milliseconds)
  2. Reversible and then irreversible adhesion and co-adhesion of the first bacteria colonisers to the conditioned surface (seconds – minutes)
  3. Multiplication of microbes to form very distinctive microbial aggregates, called microcolonies (hours – days)
  4. Maturation of the biofilm via production of more EPS and the formation of water channels (hours – days)
  5. Microbial haemostasis
  6. Ongoing detachment of microbes from the biofilm to attach to new sites (days – months)6,11

WHAT ARE THE FEATURES OF A BIOFILM?

Biofilm is a complex, organised bacterial community possessing a fine-tuned signalling system and highly sophisticated survival strategies. Regardless of the species comprising the whole, biofilm have the following basic features in common that contribute to antimicrobial resistance and make them very difficult to eradicate:

Surface Attachment

Surface Attachment

There is usually an attachment of the bacteria to a surface, such as a wound bed or medical device, which is the most potent signal for biofilm formation and serves to anchor the biofilm.12

Extracellular Polymeric Substance (EPS)

Extracellular Polymeric Substance (EPS)

A protective extracellular polymeric substance (EPS) is secreted by the biofilm to surround and encapsulate the individual microbes within the EPS matrix, shielding them from both mechanical and chemical attack. In a human host this provides protection against white blood cells, antibodies, and even therapeutic antibiotics. The slimy EPS matrix may be composed of polysaccharides, host DNA, bacterial DNA, bacteria proteins, or host plasma components. To confront different treatments or threats, the biofilm is highly adaptive and can alter these components to suit its needs or even change the composition of the matrix.12

Quorum Sensing

QUORUM SENSING

The development and preservation of the biofilm matrix is facilitated via a specialised cell-to-cell communication model referred to as quorum sensing, that is unique to biofilm. Bacteria exhibit social behaviour and utilise quorum sensing to enable cells of a colony or consortia to specify and modify gene expression, in turn regulating a diverse array of physiological processes. Quorum sensing relies on the production of signal molecules, called autoinducers, which are diffusible and allow the bacteria to self-regulate their own population. Essentially, quorum sensing allows a community of single cell bacteria to behave as a cooperative, multicellular organism, diversifying its metabolic processes and enhancing its survival mechanisms.3,13

Reconstitution

RECONSTITUTION

Biofilm can reconstitute itself after a catastrophic event, such as debridement or antimicrobial treatment, that destroys almost all its member bacteria. The remaining fragments, protected by the EPS matrix, will reattach, become metabolically active and then signal through quorum sensing pathways to rise up and reconstitute the biofilm in the exact same host niche. Fortunately, while the biofilm reconstitutes itself it is more vulnerable to host immunity and treatment, thus creating a therapeutic window for treatment to eliminate the biofilm.12

THE EPS

80-90% of a biofilm is composed of the EPS.15 The EPS surrounds and encapsulates the individual bacteria within the EPS matrix, providing a highly adaptive, protective shield for the colony against mechanical and chemical attack.

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