Different sensitivity levels to norspermidine on biofilm formation in clinical and commensal Staphylococcus epidermidis strains

Biofilm formation on medical and surgical devices is the main virulence factor of Staphylococcus epidermidis. A recent study has shown that norspermidine inhibits and disassembles the biofilm in the wild-type Bacillus subtilis NCBI3610 strain. In this study, the effect of norspermidine on S.epidermidis biofilm formation of clinical or commensal strains was tested. Biofilm producing strains of S.epidermidis were isolated from healthy skin (HS; n=3), healthy conjunctiva (HC; n=9) and ocular infection (OI; n=19). All strains were treated with different concentrations of norspermidine, spermidine, putrescine, and cadaverine (1, 10, 25, 50 and 100μM), and the biofilm formation was tested on microtiter plate. Besides, cell-free supernatants of S.epidermidis growth at 4h and 40h were analyzed by gas chromatography coupled to mass spectrometry (GC-MS) to detect norspermidine. Results showed that norspermidine at 25μM and 100μM prevented the biofilm formation in 45.16% (14/31) and 16.13% (5/31), respectively; only in one isolate from OI, norspermidine did not have effect. Other polyamines as spermidine, putrescine and cadaverine did not have effect on the biofilm formation of the strains tested. Norspermidine was also capable to disassemble a biofilm already formed. Norspermidine was detected in the 40h cell-free supernatant of S.epidermidis by GC-MS. Norspermidine inhibited the biofilm development of S.epidermidis on the surface of contact lens. In this work, it was demonstrated that S.epidermidis produces and releases norspermidine causing an inhibitory effect on biofilm formation. Moreover, this is the first time showing that clinical S.epidermidis strains have different sensitivity to norspermidine, which suggest that the composition and structure of the biofilms is varied. We propose that norspermidine could potentially be used in the pre-treating of medical and surgical devices to inhibit the biofilm formation.