
Biofilms are a population of cells that grown attached to a surface involved in exopolysaccharide matrix which protects them from attack by antibiotics or immune system. Many chronic and persistent infections are caused by bacterial biofilms, which increase significantly the resistance to antimicrobials. Different mechanisms of resistance have been proposed such as: synthesis of extracellular polymers (physical barrier effect), enzymatic modification of antimicrobials, decrease of bacterial growth rate, phenotypic changes in bacterial cells (as a result of the acquisition of resistance genes within the biofilm), and the persistence of a small group of cells in the bacterial community. But all is not bad in life, bacterial biofilms also may have a protective role, for example the normal flora.