In vitro activity of available antimicrobial coated Foley catheters against Escherichia coli, including strains resistant to extended spectrum cephalosporins.

We determined the activity, comparative potency and effect durability of commercially available, antimicrobial coated Foley catheters against Escherichia coli isolates, including extended spectrum cephalosporin resistant strains. We used an inhibition zone assay (diffusible inhibition) and an adherence assay (diffusible and contact dependent inhibition) to assess the inhibitory effect of 3 currently marketed antimicrobial coated catheters, including 2 coated with silver and 1 coated with nitrofurazone, and corresponding silicone catheters against 9 E. coli strains, including 7 extended spectrum cephalosporin resistant and 2 extended spectrum cephalosporin susceptible strains, and a Pseudomonas aeruginosa reference strain. In each assay the nitrofurazone coated catheter showed the greatest and most durable (through day 5) inhibitory activity. This was comparable for extended spectrum cephalosporin resistant and extended spectrum cephalosporin susceptible E. coli strains but decreased or absent for the Pseudomonas strain. One of the 2 silver coated catheters showed sparse but measurable inhibition zone activity on day 1 but not thereafter and no statistically significant activity on adherence assay. The other lacked detectable activity using either test system. In the adherence assay the nitrofurazone coated catheter decreased the E. coli count as potently in inoculum broths as in post-sonication suspensions (median decrease more than 8 and more than 6 log(10) cfu/ml, respectively). The nitrofurazone coated catheter showed significantly greater in vitro potency and durability of the antimicrobial effect against 9 E. coli strains than the 2 silver coated catheters, of which 1 appeared completely inert. No difference in antimicrobial effect was apparent between extended spectrum cephalosporin resistant and susceptible E. coli. The clinical relevance of these in vitro findings remains to be defined.