Biofilm is defined as a microbiologically derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or each other, and embedded in a matrix of extracellular polymeric substances (EPS) that they have produced. This matrix accounts for about 90% biomass, exhibiting an altered phenotype with respect to growth rate and gene transcription. Environmental changes are responsible for the transition from planktonic growth to biofilm and cause changes in the expression of surface molecules, virulence factors, and metabolic status, allowing the bacteria to acquire properties that enable their survival in unfavourable conditions.
Biofilm are ubiquitous and can be found in a wide variety of sites or niches. They can be formed by one or multiple bacterial species forming complex structures and they are currently estimated to be responsible for over 65% of nosocomial infections and 80% of all microbial infections.
Biofilm formation is carried out in five steps:
i) Reversible attachment of planktonic bacteria to surfaces.
ii) Irreversible attachment to surfaces.
iii) Formation of a complex layer of biomolecules and EPS secretion that constitute the external matrix.
iv) Biofilms acquire a three-dimensional structure when they reach maturity.
v) When biofilms are fully mature, detachment may occur.