Objectives: Antimicrobial lock solutions are used for prevention and management of catheter-related bloodstream infections. ML8-X10 (a prototype oil-in-water micro-emulsion based on a novel free fatty acid), vancomycin/heparin and taurolidine/citrate/heparin (Taurolock TM -Hep500) lock solutions were tested against biofilm-forming Staphylococcus epidermidis and methicillin-susceptible Staphylococcus aureus. Methods: MICs were tested in neutral broth (pH 7) and acidified broth (pH 5). In an

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... lished in vitro central venous catheter (CVC) lock model, solutions were introduced after 24 h of bacterial growth in a CVC incubated at 378C. After an additional 8, 24 or 72 h of incubation, saline flush and cut catheter segments were processed for bacterial quantification. The cfu/mL at 0 h was subtracted from cfu/mL at the different timepoints. Results: The activities of ML8-X10 and taurolidine solutions were enhanced at lower pH (P,0.05). Against S. epidermidis, ML8-X10 solution demonstrated less activity than taurolidine at 8 h (P,0.001), but was not significantly different from vancomycin. At 24 h, ML8-X10 solution demonstrated significantly less activity than taurolidine (P,0.001), but was significantly more active than vancomycin (P,0.001). Against S. aureus, ML8-X10 solution was less active than taurolidine at 8 and 24 h (P,0.001 for both), but was similar to vancomycin. At 72 h, all lock solutions reduced colony counts to levels that approached or reached the limit of detection against both strains. Conclusions: In our in vitro catheter lock model, the novel free fatty acid emulsion demonstrated activity against biofilm-forming staphylococci similar to or greater than that of vancomycin lock solution. Taurolidine was the most active lock solution at 8 and 24 h, with all lock solutions tested demonstrating high activity at 72 h.