Inhibition of Bacterial Attachment on Surfaces by Immobilization of Tobramycin-Loaded Liposomes

Stainless steel surfaces were processed by gold deposition in order to immobilize tobramycin-loaded liposomes which were functionalized on their surface with thiol-groups (through maleimide (MAL) derivatization with thiols). After optimizing the tobramycin loading in liposomes (LIPs), and the immobilization of THIOL-MAL-functionalized LIPs on gold-sputtered surfaces, the coated surfaces were challenged with two reference Staphylococcus epidermidis strains: ATCC 35984 (slime-positive) and ATCC 12228 (slime-negative), in order to measure the degree of surface protection from biofilm formation. Moreover, the effect of the reference and two well characterized clinical S. epidermidis strains on the integrity of LIPs (composed of PC or DSPC) was evaluated, in order to investigate whether specific interactions between LIPs and bacteria occur, and if they are affected by LIP membrane composition and/or bacterial strain type. Bacteria growth on surfaces is substantially inhibited by TOBR-loaded-LIP immobilization, especially in the case of the non-biofilm forming bacterial strain. Gold sputtered surfaces were moderately (albeit significantly) protected, from both reference strains tested (compared to bare surfaces). Interestingly, LIP integrity is significantly decreased in the presence of bacteria (at specific lipid/bacteria ratios); the biofilm-forming bacteria being most potent for LIP disruption, whereas, less rigid liposomal membranes (PC) are affected more compared to rigid (DSPC) ones. The clinical strains are also reactive against LIP. This interaction indicates a potential for triggered release of LIP-encapsulated drugs in presence of biofilm-forming bacteria, therefore LIP encapsulation/immobilization may be envisioned as a potential platform technology for triggered antimicrobial therapy.