Effects of lipid emulsion on the formation of Escherichia coli –Candida albicans mixed species biofilm on PVC

Patients receiving lipid emulsion have an increased risk of central venous catheter-related bloodstream infections (CRSBI) in the clinic. More than 15% of CRBSI are found to be polymicrobial. The objective of the study was to explore the mechanism and effects of lipid emulsion on the formation of Escherichia coli - Candida albicans mixed species biofilm (BF) on the surface of polyvinylchloride (PVC) materials. Mixed BFs were achieved by co-culturing Escherichia coli ( E.coli ) and Candida albicans ( Ca ) with PVC in various concentrations of lipid emulsion respectively. Crystal violet (CV) staining and XTT assay were performed to test the formation of BFs and the viability of bacteria in BFs. The microstructures of BFs were observed by a combined approach of fluorescence in situ hybridization (FISH), confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM). The study found that lipid emulsion promoted the formation of Escherichia coli-Candida albicans mixed biofilm, especially 10% lipid emulsion. The mechnism of lipid emulsion prompting mixed biofilm formation may be significantly up-regulating the expression of flhDC, iha, HTA1, and HWP1 genes associated with bacterial motility, adhesion and biofilm formation. For prevention of central venous catheter-associated infections, medical professionals should maintain strict aseptic precautions when handling lipid emulsion and avoid using high concentrations of lipid emulsion for a long time as much as possible. The study provides interesting information for future research in biomaterial related infection.