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Impact of chlorhexidine-silver sulfadiazine-impregnated central venous catheters on in vitro quantitation of catheter-associated bacteria

To assess the impact of the antiseptic effects of silver sulfadiazine-chlorhexidine-impregnated central venous catheters on catheter culture systems, a series of in vitro experiments was performed. Segments of antiseptic and non-antiseptic-impregnated catheters were sonicated in thioglycolate broth and removed. After the addition of 10(3) CFU of Staphylococcus epidermidis per ml, aliquots of catheter-exposed broth were subcultured onto blood agar at 15-min intervals. Decreased mean colony counts were noted at 45 min for broth exposed to antiseptic-impregnated catheters compared with the colony counts for broth exposed to non-antiseptic-impregnated catheters (170 versus 540 CFU/ml). These effects, which were also demonstrated by the roll-plate method, were abrogated by the use of medium containing inhibitors of silver sulfadiazine and chlorhexidine. To assess the duration of the antiseptic effects, catheter segments were suspended for up to 14 days in phosphate-buffered saline, incubated with 10(6) CFU of S. epidermidis per ml, and cultured. Inhibition of bacterial growth by antiseptic-impregnated catheters disappeared after 14 days. These studies suggest that antiseptic compounds elute from catheters during broth- and solid medium-based culturing processes, making necessary the addition of inhibitors of these compounds in culture media. They further suggest that the antimicrobial effects of antiseptic-impregnated catheters wane within several days of placement.