Bacterial biofilm

Introduction to biofilms

The study of biofilms represents a new way of understanding the microbiology of virtually everything around us, from problems which affect industries to serious public health issues.

Microbial biofilms are widely present in nature where this kind of growth is the usual form of bacterial growth. We can encounter biofilms everywhere, and their presence has a huge impact on various aspects of our lives. For example, the plaque that forms on the teeth and causes tooth decay is one type of bacterial biofilm; the mucous material that covers a vase in which we have deposited flowers and the gunk that clogs the household drains are also biofilms. If someone has ever walked in a stream or river, they may have slipped on rocks that were slimy with biofilm.

The ability of biofilm formation does not appear to be restricted to any specific group of microorganisms and it is now considered that all microorganisms are capable of forming biofilms in appropriate environmental conditions

What are biofilms?

Biofilms are defined as sessile communities characterized by cells that are irreversibly attached to a surface or to each other, embedded in a matrix of extracellular polymeric substances (EPS), and that exhibit differential phenotypic characteristics with respect to their planktonic counterparts. Under such growth conditions exopolysaccharide production is often increased, which could form a exopolymer slime layer and protect the bacteria against a variety of antimicrobial agents as well as against host attack. A biofilm is composed of living, reproducing microorganisms, such as bacteria, which exist as a colony, or community.

A biofilm community can be formed by a single kind of microorganism, but in nature biofilms almost always consist of mixtures of many species of bacteria, as well as fungi, algae, yeasts, along with non-living debris and corrosion products. For example, over 500 bacterial species have been identified in typical dental plaque biofilms.

How do biofilms form?

A biofilm forms when microorganisms adhere to the surface of some object in a moist environment and begin to reproduce. Biofilms grow virtually everywhere, in almost any environment where there is a combination of moisture, nutrients, and a surface. Biofilms can form on just about any imaginable surface, like metals, plastics, natural materials (such as rocks), medical implants, kitchen counters, contact lenses, human and animal tissues.

The biofilm life cycle

• Attachment: the first stage of the biofilm formation process is the adhesion to the surface. Free-floating, or planktonic, bacteria encounter a submerged surface and soon become attached. At first reversible adhesion occurs and finally the irreversible adhesion of bacteria to the surface takes place. They begin to produce extracellular polymeric substances (EPS) and to colonize the surface.
• Growth: the bacteria begin to reproduce and form microcolonies. EPS production, which constitutes the matrix of biofilm, allows the emerging biofilm community to develop a complex, three-dimensional structure that is influenced by a variety of environmental factors. The composition of the EPS is different for each bacterium.
• Dispersal: finally, after biofilms have reached maturity, they can propagate through detachment of small or large clumps of cells, which allows bacteria to attach to a surface or to a biofilm away from the original community.

How do biofilms impact our World?

Biofilms are a natural part of the ecology of the earth. Many biofilms are quite harmful (for example, when they produce infections in wounds) and must be treated or controlled. Other biofilms are beneficial and can be used to solve serious problems (such as ground contamination from an oil spill).

Biofilms have been found to be involved in a wide variety of microbial infections in the body. Over 60% of all microbial infections are caused by biofilms. Biofilms have been implicated in such common problems as urinary tract infections, catheter infections, middle-ear infections, formation of dental plaque, gingivitis and coating contact lenses. All these infections have in common that they are chronic in nature and very persistent. They are highly resistant to antimicrobial treatments and host defense. This is what mainly distinguishes acute from chronic infections. While acute infections can be removed after a short treatment of antibiotics, biofilm infections usually are never completely eliminated, resulting in recurrent episodes. This is because the bacteria in the biofilm can be up to 1,000 times more resistant to antibiotics than the same bacteria grown in liquid medium.

Domestically, kitchens and bathrooms are the preference sites for the establishment of biofilms. It is no coincidence that in these sites the traditional hygienic procedures are based on mechanical processes helped by detergents and disinfectants. In the case of dental plaque, mouthwashes only help to displace the freshly deposited organic matter. The tenacity with which biofilms adhere to surfaces is the property which makes cleaning difficult. This is because the cells produce EPS, which form very adhesive gels with water, and which encompasses the cells and binds them to the surface.