David Blicq  dblicq@rrc.mb.ca  (update 01/04/2010)         DIRECTORY I BIO I NOTICE BOARD

Biofilm Basics

In their natural environment, bacteria often grow as populations attached to surfaces in complex structures called biofilms. These Biofilms are aggregates of bacteria encased in a mucoid polysaccharide structure which attaches the community to a surface. Biofilms can form on and adhere to nearly any surface: examples include plaque on teeth, piping / plumbing, catheters, medical devices, etc. A biofilm may be a pure culture derived from a single type of microorganism or (more commonly)  a mixed culture of multiple microorganisms. Once established, biofilm populations cause a number of reactions (many considered detrimental, some beneficial).

Biofilm Formation

Biofilm formation begins when free-living, (planktonic) bacteria encounter a surface. There are several stages in film formation from free aquatic to adherent and stationary:

http://www.feridescroniques.com/presentacions/Limpieza%20y%20desbridamiento%20PDF.pdf

1. initial adsorption to surface
2. cell-cell growth population growth / reproduction
3. production of an extracellular polysaccharide substances / irreversible adhesion
4. trapped biolfilm bacteria form a community that controls the structural complexity of the biofilm

Factors affecting Adhesion  

	nature and type of surface / environment
	surface shape / homogeneity
	charge / lack of surface charges
	hydrophobicity
	hydrodynamics / flow characteristics

Benefits of Biofilm formation to Bacteria

	Stationary growth in a  hospitable environment
	Resistance to antibiotics, anti-fouling agents etc. (limited toxin penetration)
	Synergism between species and metabolisms
	Domination of immediate environment

 Environmental Biofilms

	Sewage treatment bioreactors
	Root nodules of legumes
	Termite, ruminant digestion
	Water pipes
	Contact lens cases

Infectious Disease Biofilms

	Cystic Fibrosis
	Dental plaques / dental diseases
	Endocarditis
	Urinary catheter
	Biomedical implants

Factors affecting Biofilm growth

	Rate-limiting nutrient penetration (culture and environment-dependant)
	Nature of anaerobic and aerobic areas within biofilm
	Heterogeneous versus homogeneous populations

Problems caused by Biofilm Formation

	Damage to industrial equipment
	Contamination of food, pharmaceutical and medical products
	Energy loss through inefficient energy transfer
	Medical infections and antibiotic resistance

Controlling Biofilms

Traditional "effective" concentrations of antibacterial / antibiotic agents are established using ideal laboratory conditions with liquid cultures of free cells. This allows for excellent physical contact and uniform exposure  to cells that are highly active metabolically. In a biofilm, it is often impossible to have any antibiotic penetrate to the original surface. "Biofilms can require 100 to 1,000 times the concentration of an antibiotic to control an infection".   As well, slow growing / dormant microorganisms are far lee susceptible to antimicrobial agents as compared to viable, log-stage growth cycles.

 Antifouling Surfaces

Researchers are highly interested in creating and anchoring non-biofouling materials as implants and biomedical devices. The overall strategy is to design materials which eliminate the environmental opportunities for microbial adhesion and subsequent biofilm formation. In addition to the obvious benefits of biofim-resistant medical materials, there are many other applications: self-cleaning pipes / plumbing, non-fouling aquatic surfaces, etc.

Potential Uses of Biofilms (industrial / environmental)

1. Bioremediation of hazardous materials and waste sites

2. Biofilteration of industrial waste water

3. Formation of natural biological barriers to protect soil and groundwater from contamination.