To preliminarily test the antimicrobial prevention effect of the e-catheters, four clinical isolates derived from catheter-associated infections were studied, S. aureus IDRL-10296, S. epidermidis NRS34, E. faecium IDRL-11625, and E. coli IDRL-7343. Bacterial inocula were selected to target a concentration of >8 log10 CFU/ml after 48 h in blank catheters. An initial bacterial concentration of 104 CFU/ml was used for S. aureus IDRL-10296, 107 CFU/ml for S. epidermidis NRS34, 105 CFU/ml for E. faecium IDRL-11625, and 104 CFU/ml for E. coli IDRL-7343. Different inoculum sizes were used to establish 48-h concentrations that would allow determination of a 3-log reduction in bacterial concentrations between treatment groups.
Bacteria were subcultured from frozen aliquots onto BBL Trypticase soy agar (TSA II) with 5% sheep blood plates (Becton, Dickinson, Franklin Lakes, NJ) and incubated at 37°C overnight. One bacterial colony from this first plate was then subcultured on a second TSA II plate for 24 h. One to three colonies from this second plate were added to 2 ml of Trypticase soy broth (TSB) and incubated for 2 h at 37°C on an orbital shaker at 120 rpm to reach a 0.5 McFarland standard (∼1.5 × 108 CFU/ml). The bacterial suspension was then diluted in TSB to the targeted bacterial inoculum concentration for each isolate (see above).
Bacteria were subcultured from frozen aliquots onto BBL Trypticase soy agar (TSA II) with 5% sheep blood plates (Becton, Dickinson, Franklin Lakes, NJ) and incubated at 37°C overnight. One bacterial colony from this first plate was then subcultured on a second TSA II plate for 24 h. One to three colonies from this second plate were added to 2 ml of Trypticase soy broth (TSB) and incubated for 2 h at 37°C on an orbital shaker at 120 rpm to reach a 0.5 McFarland standard (∼1.5 × 108 CFU/ml). The bacterial suspension was then diluted in TSB to the targeted bacterial inoculum concentration for each isolate (see above).