Descrição
Medical device-associated infections caused by pathogens such as Staphylococcus epidermidis might involve
biofilm formation and those are particularly challenging. The involvement of antibiotic resistant Staphylococci,
exacerbates the problem. Rifampicin cannot be used as a single agent to treat infections because of the rapid
selection of resistant mutants. However, combinations of rifampicin with other anti-staphylococcal agents
could prevent the emergence of rifampicin resistance during therapy. N-acetylcisteine (NAC) decreases biofilm
formation by a variety of bacteria and reduces the production of extracellular polysaccharide matrix. The goal
of this study was to assess the antimicrobial activity of NAC in combination with rifampicin against biofilm
of S. epidermidis. Two S. epidermidis strains biofilm-producing (9142 and 1457) were used in this study.
1xMIC (4mg/ml) and 10xMIC (40mg/ml) of NAC and 10mg/l of rifampicin, based on preliminary in vitro data,
were added to 24h biofilm cells. Biofilm susceptibility to tested antimicrobial agents was assessed through
scanning electron microscopy, crystal violet staining (total biofilm biomass) and cellular viability through XTT
and colony forming units (CFU). The effect of NAC 1xMIC was similar to that of the control. Rifampicin, NAC
10xMIC alone and NAC-rifampicin combination (independently of NAC concentration used) showed significant
bactericidal effect, promoting a 3-4 log10 decrease in biofilm cells. In conclusion, the results didn’t point to any
synergistic effect between the two agents. Nevertheless, NAC seems to be a possible alternative to antibiotics
in the treatment of infections associated to S. epidermidis biofilm.
; Gomes, F. I. 
