Use of central venous catheters (CVC) impregnated with minocycline and rifampin reduces the density of bacterial growth on catheters and decreases the incidence of catheter-related bloodstream infections (CRBSI). Questions have been raised over the possibility that the use of these catheters will select for antibiotic resistant organisms. We hypothesized these catheters would not predispose to such resistance.
Catheter segments (1.0 cm) were placed on the surface of agar plates previously inoculated with bacterial suspensions such that a subconfluent lawn of colony growth would be apparent after 24 h incubation at 35°C in air. Test organisms included ATCC type strains of Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. Zones of inhibition of colony growth surrounding catheters were measured at 24h intervals up to 7 days. Colonies on agar surfaces located at varying distances from catheter segments were examined for minocycline and rifampin resistance following various periods of exposure. In addition, selected colonies were subsequently exposed to minocycline or rifampin in broth and examined for selection of minocycline or rifampin resistance.
Inhibitory zones of 14–47 mm were observed with S. aureus, S. epidermidis, E. faecalis, and E. coli. Growth of P. aeruginosa was not inhibited by CVC segments. Testing of colonies of the first four organisms at various distances from CVC segments after varying periods of exposure revealed only a single instance of the emergence of resistance (e.g. S. aureus versus rifampin). Recovery of resistant clones was enhanced with minocycline or rifampin broth selection; however, a direct link between CVC exposure and resistance induction was not statistically established.CONLUSIONS: These results suggest that exposure of Gram positive cocci to either rifampin or minocycline alone can lead to the development of resistance; however, the risk of developing resistance is low when bacteria are exposed to this antibiotic combination impregnated in CVC.
The risk of the development of bacterial resistance to minocycline/rifampin impregnated catheters is low.
S.O. Heard, Cook Critical Care, Grant monies.