Influence of antibiotics on Staphylococcus epidermidis biofilms

Abstract

Staphylococcus epidermidis is a member of the coagulase-negative staphylococci and has gained substantial interest in recent years because it has become the most frequently cause of infections related to indwelling medical devices. Since S. epidermidis is resistant to some antibiotic treatments, it is of major importance to understand the mechanisms and the bacterial components involved in those mechanisms. Therefore, the present dissertation aimed to understand the mechanisms and the bacterial components involved in the antibacterial resistance mechanisms. The first goal of this work was the evaluation of the activity of different groups of antibiotics, such as cell-wall and protein synthesis inhibitors, on S. epidermidis biofilms. Changes on S. epidermidis biofilms were evaluated regarding the total biofilms biomass, bacteria viability and biofilm’s matrix changes after treatment. The second goal of this work was the evaluation of the influence of antibiotics on the matrix composition considering the contribution of PIA and extracellular DNA to the changes referred. Antibiotics treatment with the glycopeptides, vancomycin and teicoplanin, had an effect on significantly increasing the total biofilm biomass on all strains. Even though these antibiotics were effective against biofilm associated bacteria assessed by XTT, by DMMB staining method it become obvious that they had an effect on increasing the amount of biofilms matrix. Thus imply that they promoted the membrane rupture, enhancing PIA’s production and the formation of a rougher biofilm. Results found on the combinated treatment of DNase I plus antibiotics indicated that destruction of eDNA by DNase I leads to a decrease in the matrix, and as a result, antibacterial agents protein inhibitors, such as rifampicin and gentamicin, act more effectively to reduce the biofilm biomass. In conclusion, it was possible to evaluate that antibiotic agents promoted alterations on S. epidermidis biofilms. It was also possible to conclude that S. epidermidis biofilms from different strains showed an enhanced resistance to the application of treatment with glycopeptide antibiotics. Those antibiotics are normally reserved for use against multi-resistant staphylococci, however from this study data, it is of major importance to have a better understanding of the resistance mechanisms and to find different alternatives.