Detection of biofilm-forming strains of Staphylococcus epidermidis and S. aureus.

The formation of biofilm represents an important virulence factor of certain strains of Staphylococcus epidermidis and S. aureus. The ability of bacteria to aggregate, forming biofilms, is strictly related to the capacity of producing an extracellular mucoid substance often referred to as slime, whose main component is of polysaccharidic nature and consists of glycosaminoglycans. In recent years, new molecular techniques based on PCR have come alongside more traditional methods for identification of virulent biofilm-forming strains. The detection of the genes governing the production of such extracellular polysaccharide and, in particular, the icaA, the icaC and the icaD genes, provides us with a rapid and accurate technique for strain characterization. However, well-established methods, such as the Congo red agar test are still needed in order to confirm the phenotypic expression in the case of possible phase-variant strains. In future, the complete knowledge of the genetic mechanisms of phenotype modulation, comprehending all regulatory genes, could permit the characterization of the isolates just by molecular means in a single step.