Cell surface hydrophobicity, biofilm formation, adhesives properties and molecular detection of adhesins genes in Staphylococcus aureus associated to dental caries

Staphylococcus aureus is an important pathogen that forms biofilm. In this study, 22 S. aureus have been isolated from the oral cavity of Tunisian children and investigated for slime production using Congo red agar method (CRA) and semi quantitative adherence assay. The hydrophobicity of strains was evaluated by the microbial adhesion to solvent (MATS) test. The adherence of S. aureus to Hep2 cells was examined by light microscopy. The genes implicated in adhesion (icaA, icaD, fnbA, cna, clfA) were detected. Polymerase chain reaction was used. The affinity to hexadecane was low proving a hydrophilic character of all the studied strains. Qualitative biofilm production revealed that 50% of strains were slime producers. The result of OD(570) showed that four strains isolated from the caries-active children were highly biofilm positive. In addition, 50% of strains were icaA and icaD positive. The fnbA gene was present in 59.1% of isolated strains. Furthermore, 54.5% of strains harboured the cna gene, 9.1% were clfA positive and 50% were hla positive. Quantitative adherence varied considerably among the tested strains. All strains showed adherence to Hep2 cells. However, the level of adhesion varied between strains as follows. Seven strains were defined as moderately adherent, nine as strongly adherent and six as weakly adherent. The percentage of infected cells ranged from 15+/-0.0376 (B374) to 96+/-0.019 (B295) and the total number of bacteria per 100 cells ranged from 15+/-5.1 (B374) to 1824+/-30.1 (B295).