Comparative analysis of PIA-negative Staphylococcus epidermidis biofilm formation and destruction under hydrolytic factors
The ability of Gram-positive bacteria Staphylococcus epidermidis to adhere to and form biofilm on various polymeric and metallic surfaces of indwelling medical devices results in the fact that now these bacteria are one of the most common causes of serious nosocomial infections. Although the adhesion is an essential part of biofilm formation the primary contact between the bacterial cells and the solid surface do not always lead to a strong fixation of bacteria on it. Therefore, the comparison of the hydrolytic enzymes and sodium periodate influenced the bacterial adhesion (30 min) and biofilm formation (24 h), and the destruction of the already formed biofilm S. epidermidis occured. According to Congo red agar assay, all tested S. epidermidis strains lacked the ability to produce polysaccharide intercellular adhesion and polymer of N-acetylglucosamine which promotes the biofilm formation on solid surfaces. Adhesion and biofilm formation of all studied strains were strongly inhibited by trypsin (15-52% of control), lysozyme (35-65%), DNase (18-70%) and sodium periodate (17-55%), except S. epidermidis ATCC 29887, the biofilm formation of which was similar to control at the DNase presence. Although the extracellular DNA plays an important role in the bacterial colonization, the addition of the cattle DNA did not affect all stages of biofilm development for all used strains. The preformed biofilm of all studied strains was resistant to the lysozyme and the sodium periodate as their biofilm matrix do not contain the PIA. At the same time, S. epidermidis ATCC 29887 biofilm was destroyed after treatment with trypsin (56±8%) and DNase (63±16%), and S. epidermidis GISK 33 biofilm - after the RNase treatment (70±11%). However, the effect of RNase differed between strains as well as between the moments of its introduction into the medium. Adding RNase simultaneously with inoculum stimulated adhesion of S. epidermidis ATCC 12228 (143±32 %) and inhibited biofilm formation of S. epidermidis ATCC 29887 (63±24 %). Our results show that the relationship between the sensitivity of mature biofilm to the treatment by hydrolytic factors such as enzymes and the influence of these factors on the biofilm formation is not linear. On the contrary, the processes of attachment of bacterial cells and subsequent biofilm formation are directly interdependent.