Biofilms and Device-Associated Infections

Central Venous Catheter Biofilms

Scanning and transmission electron microscopy has shown that virtually all indwelling central venous catheters are colonized by microorganisms embedded in a biofilm matrix^[5]. The organisms most commonly isolated from catheter biofilms are Staphylococcus epidermidis, S. aureus, Candida albicans, P. aeruginosa, K. pneumoniae, and Enterococcus faecalis^[6,7].

These organisms originate from patient's skin microflora, exogenous microflora from health-care personnel, or contaminated infusates. They gain access to the catheter by migration externally from the skin along the exterior catheter surface or internally from the catheter hub or port^[8]. Colonization of these devices can occur rapidly (within 24 hours) and may be a function of host-produced conditioning films (platelets, plasma, and tissue proteins)^[8]. Raad et al.^[9] found that biofilm formation on central venous catheters was universal, but the extent and location of biofilm formation depended on the duration of catheterization: short-term (<10 days) catheters had greater biofilm formation on the external surface; long-term catheters (30 days) had more biofilm formation on the catheter inner lumen. The nature of the fluid administered through central venous catheters may affect microbial growth: gram-positive organisms (S. epidermidis, S. aureus) did not grow well in intravenous fluids, whereas the gram-negative aquatic organisms (e.g., P. aeruginosa, Klebsiella spp., Enterobacter spp., Serratia spp., and Pantoea sp.) sustained growth^{[10,11,12,13,14]}. Because many of these solutions have limited nutrients, bacterial growth rarely produces turbidity, meaning that numbers are <10⁷ organisms per milliliter. The number of organisms on the catheter tip is related to occurrence of bloodstream infection in the patient^[7,15,16,17], supporting the concept of a critical level of biofilm development above which substantial cell detachment and embolism occur.

Several studies have examined the effect of various types of antimicrobial treatment in controlling biofilm formation on these devices. Freeman and Gould^[18] found that addition of sodium metabisulfite to the dextrose-heparin flush of the left atrial catheter eliminated microbial colonization of these catheters. Darouiche et al.^[19] found that catheters impregnated with minocycline and rifampin were less likely to be colonized than those impregnated with chlorhexidine and silver sulfadiazine. In a study by Kamal et al.^[20], catheters coated with a cationic surfactant (tridodecylmethylammonium chloride), which was in turn used to bond cephalosporin to the surface, were less likely to become contaminated and develop biofilms than were untreated catheters. Flowers et al.^[21] found that an attachable subcutaneous cuff containing silver ions inserted after local application of polyantibiotic ointment conferred a protective effect on catheters, resulting in lower rates of contamination. Maki^[8] suggested several ways to control biofilms on central venous catheters, including using aseptic technique during implantation, using topical antibiotics, minimizing the duration of catheterization, using an in-line filter for intravenous fluids, creating a mechanical barrier to prevent influx of organisms by attaching the catheter to a surgically implanted cuff, coating the inner lumen of the catheter with an antimicrobial agent, and removing the contaminated device.

Emerging Infectious Diseases. 2001;7(2) © 2001 Centers for Disease Control and Prevention (CDC)