Upregulation of icaA, atlE and aap genes by linezolid but not vancomycin in Staphylococcus epidermidis RP62A biofilms

Biofilms are complex bacterial structures protected by a self-produced polymer matrix that enables survival in hostile environments. Biofilms are more resistant to antibiotics than their planktonic counterparts and are therefore more difficult to eradicate. The aim of this study was to investigate the influence of vancomycin and linezolid on the maintenance of staphylococcal biofilms and their effect on the expression of biofilm-associated genes in Staphylococcus epidermidis. Pre-formed biofilms of S. epidermidis RP62A were challenged with linezolid and vancomycin at different concentrations as well as at their clinically relevant target concentration (15 mg/L) over time. Expression of icaA, atlE, aap, rnaIII, luxS, sarA, rsbU and icaR genes following 2 h of exposure to these antibiotics was determined by quantitative PCR. Vancomycin did not significantly affect the biofilm under the tested conditions. However, linezolid affected the biofilm structure at concentrations of ≥2 mg/L (P < 0.05); moreover, the exposure time to this antibiotic was a determinant for biofilm eradication. The level of transcription of icaA, aap and atlE increased by 5.18-, 2.58- and 3.06-fold, respectively, in biofilms exposed to linezolid, but no changes were observed for vancomycin. The other genes were not affected by these antibiotics. This study demonstrated that linezolid was effective in eradicating biofilms formed by S. epidermidis RP62A. Under the conditions tested, linezolid upregulated biofilm-associated genes probably due to the stress caused by low-dose antibiotic stimulation. In this study, linezolid showed better performance than vancomycin against staphylococcal biofilms.