Heterogeneity of Biofilm Formation Among Staphylococcus aureus and Coagulase-Negative Staphylococcus Species in Clinically Relevant Intravenous Fat Emulsions

<b>Background</b>: Compared to soybean oil intravenous fat emulsion (SO-IFE), use of mixed-oil IFE (MO-IFE) is associated with reduced rates of catheter-related bloodstream infections caused by coagulase-negative <i>Staphylococcus</i> species (CoNS) in pediatric patients receiving parenteral nutrition. <b>Methods</b>: Using an in vitro biofilm model, this study aimed to assess the impact of IFEs on biofilm formation among <i>Staphylococcus</i> species. <i>S. aureus</i>, <i>S. capitis</i>, <i>S. epidermidis</i>, <i>S. haemolyticus</i>, <i>S. hominis</i>, and <i>S. lugdunensis</i> were cultivated as biofilms in media supplemented with SO-IFE, MO-IFE, or fish oil IFE (IFE). Biomass was quantified by the crystal violet method, and follow-up planktonic growth assays assessed antimicrobial effects of IFEs. <b>Results</b>: Compared to SO-IFE, MO-IFE and FO-IFE significantly inhibited biofilm formation of <i>S. aureus</i> but did not impact planktonic growth. Contrary to clinical data, CoNS biofilm formation was not impacted by any of the IFEs tested. <i>S. aureus</i> biofilm inhibition in IFEs was further investigated by comparing differences following growth in SO-IFE supplemented with capric acid, docosahexaenoic acid (DHA), or eicosapenaenoic acid (EPA) to concentrations matching those of MO-IFE. Capric acid supplementation was associated with significant reduction in biofilm formation compared to SO-IFE alone. However, this was attributed to a bactericidal effect based on follow-up planktonic growth assays. <b>Conclusions</b>: These results suggest that biofilm formation in <i>S. aureus</i> is variably impacted by fatty acid composition in clinically relevant IFEs, with capric acid exhibiting bactericidal activity against tested isolates.