Activity of ethanol and daptomycin lock on biofilm generated by an in vitro dynamic model using real subcutaneous injection ports

Vancomycin lock solution (LS) is recommended for the conservative treatment of subcutaneous injection port (SIP)-related infections, but may be associated with failure. We used an in vitro dynamic model of biofilm formation in an SIP, based on a continuous flow circulating via a real SIP, to assess the effectiveness of vancomycin (5 mg/ml), daptomycin (5 mg/ml) and ethanol 40 % LS in eradicating a pre-established Staphylococcus epidermidis biofilm. Heparin, Ringer’s lactate and enoxaparin sodium LS were used as controls. The logarithmic reductions of colony-forming units (CFU) were compared by Student’s t-test. After 24 h of exposure, the vancomycin LS did not exert a greater bactericidal effect than the heparin LS control (mean logarithmic reduction: 2.27 ± 0.58 vs. 1.34 ± 0.22, respectively, p = 0.3). The mean logarithmic reduction was greater with daptomycin LS (5.45 ± 0.14 vs. 0.39 ± 0.12, p < 0.01) and ethanol LS (6.79 ± 1.03 vs. 1.43 ± 0.54, p = 0.02). Bacterial revival after exposure to 24 h of LS was assessed. The mean viable bacteria count was significantly higher for vancomycin LS (9.36 ± 0.10 log₁₀CFU) and daptomycin LS (9.16 ± 0.02 log₁₀CFU) than for ethanol LS (2.95 ± 1.65 log₁₀CFU). Ethanol appeared to be the most attractive option to treat SIP-related infection, but its poor ability to entirely disrupt the biofilm structure may require its use in association with a dispersal agent to avoid renewal of the biofilm.