BIOFILM FORMATION BY Staphylococcus epidermidis DURING HYPEROSMOTIC STRESS

Staphylococcus epidermidis is a common pathogen in medical device-associated infections, due main to its ability to form adherent biofilm to plastic surfaces as in central venous catheters that are frequently used in critically ill patients. The biofilm formation by staphylococci is a complex process and strongly influenced by a variety of external conditions found during host tissues interactions. However, is not clear how hyperosmotic stress can affect the staphylococcal ability to form biofilms, which is an important stage in the search for new medical treatments capable of combating microorganisms that produce biofilm biomass as a resistance mechanism against drugs. Therefore, the main of this study was to provide a comprehensive insight of virulence taken by S. epidermidis during in vitro hyperosmotic conditions induced by 0.25, 0.5, 1, 1.5 M of sodium chloride (NaCl) and potassium chloride (KCl). The in vitro biofilm production was determined by crystal violet assay in a 96-well microtiter plate, over time and correlate them to the presence of hyperosmotic stress conditions. By constructing the growth curve of S. epidermidis RP62A under increasing concentrations of osmotic stressors, we found that 1.0 M and 0.5 M, respectively, provided the sub-inhibitory osmolality that slightly retarded the growth rate of S. epidermidis compared to others conditions. Results indicated that hyperosmotic treatment significantly inhibited the biofilm formation by S. epidermidis, and this inhibitory effect was concentration-dependent. In addition, hyperosmotic conditions upon 24 h old biofilms suggesting an enhanced biofilm dispersion by reduction of amount of residual biofilm biomass. Then, we evaluated the biofilm biomass after additional exposure time (18 h) to determine the biofilm detachment. The hyperosmotic conditions upon 24 h old preformed biofilms showed an enhanced biofilm dispersion by reduction of amount of residual biofilm biomass compared to 18 h. These results clearly suggest that hyperosmotic exposure reduce the biofilm biomass formation and induce dispersal of biofilm. However, extensive studies are necessary to explain the sophisticated machineries, like hypoxia and glucose and iron deprivation, used by S. epidermidis to establishment in the host environment. The proteomic analysis of secretome during hyperosmotic stress are the progress to understanding how the S. epidermidis survive in the host.