Overview of Genetic Background Beyond Polysaccharide Intercellular Adhesion Production in Staphylococcus epidermidis

An important observation during quantification experiments of Staphylococcus epidermidis biofilm is that there is a great difference in the biofilm biomass of different strains despite the same experimental conditions. This study aimed to study the genotypic background beyond differential rates of Polysaccharide Intercellular Adhesion (PIA) production in S. epidermidis biofilm forming strains. A number of 126 strains were isolated from blood cultures (n = 40), catheter cultures (n = 50), and other specimens (n = 36). The strains were obtained from patients hospitalized at the bone marrow transplant center of Tunis. Biofilm micro-plate assay, hemagglutination, and susceptibility to proteinase K methods were used to assess biofilm characteristics in the studied strains. Conventional and real time PCR were used to assess genotypic background of biofilm formation. Using PCR method, we demonstrated that there is a significant difference in ica genes (P < 0.01) and not in adhesion rsb and sar genes distribution between biofilm forming and non-biofilm forming strains. Almost all strains harbored agr type I. None of studied strains harbored IS256 inside ica operon. Ica-independent biofilm formation was detected in 11 strains that were confirmed to have proteinaceous matrix. Using Kernel density estimation, we established that biofilm biomass was higher in ica-dependent than ica-independent biofilm forming population. Using qRT-PCR, we found a significant correlation between biofilm biomass and RNAIII expression level (r2 = 0.95); but no correlation was found for biofilm biomass neither with icaA nor with ccpA genes. Data reported here indicated that there is no specific genetic combination beyond the quantity of biofilm biomass in S. epidermidis. Biofilm biomass seemed to be controlled by RNAIII expression level. Further interest should be directed to biofilm dispersal since it seems that the key difference in biofilm biomass ability of S. epidermidis strains relates to factors regulating this stage.