The Development of a Biomimetic Model of Bacteria Migration on Indwelling Urinary Catheter Surfaces

Abstract

The aim of this study was to develop a novel biomimetic in vitro extraluminal migration model to observe the migration of bacteria along indwelling urinary catheters within the urethra and assess the efficacy of a prototype chlorhexidine diacetate (CHX) coating to prevent this migration. The in vitro urethra model utilised chromogenic agar. A catheter was inserted into each in vitro urethra. One side of the urethra was then inoculated with bacteria to replicate a contaminated urethral meatus. The models were then incubated for 30 days (d), with the migration distance recorded each day. Four indwelling catheter types were used to validate the in vitro urethra model and methodology. Using the biomimetic in vitro urethra model, E. coli and S. aureus migrated the entire length of a control catheter within 24-48 h (h). In the presence of a prototype CHX coating, full migration of the channel was prevented for 30 d. The results of this study support the hypothesis that catheter-associated urinary tract infections (CAUTIs) could be prevented by targeting catheter-mediated extraluminal microbial migration from outside of the urinary tract into the bladder.

Keywords: bacterial migration; biomimetic model; catheter-associated urinary tract infections; in vitro model; urethral catheterisation.

Figure 1

In vitro extraluminal migration model: end elevation (a), front elevation (b), planar view (c) and planar image (d).

Figure 1

In vitro extraluminal migration model: end elevation (a), front elevation (b), planar view (c) and planar image (d).

Figure 2

In vitro extraluminal migration model concept and methodology.

Figure 2

In vitro extraluminal migration model concept and methodology.

Figure 3

Illustration of the serial plate transfer test (SPTT) method: (a) inoculation of entire agar surface, (b) placing of catheter samples into wells in agar surface, (c) zones of inhibition around samples after incubation.

Figure 4

Extraluminal migration of E. coli ATCC 25922 on UNCs (a, left, ▽) and −CHX (a, right, ■), +CHX (b, left, ○) and +CHX50 (b, right, ▲) catheters over 30 days. Bacterial growth is E. coli grown in Harlequin™ E. coli/Coliform Agar (a,b). Error bars represent standard error of the mean (n = 6). **** p ≤ 0.0001.

Figure 5

Extraluminal migration of S. aureus NCTC 12981 on UNC (a, left, ▽) and −CHX (a, right, ■), +CHX (b, left, ○) and +CHX50 (b, right, ▲) catheters over 30 days. Bacterial growth is S. aureus grown in CHROMagar™ Staph aureus agar (a,b). Error bars represent standard error of the mean (n = 6). **** p ≤ 0.0001.

Figure 6

Images of the serial plate transfer test for +CHX catheter when exposed to S. aureus NCTC 12981 (a, △) and E. coli ATCC 25922 (b, ●). Error bars represent standard deviation, n = 6.

Figure 7

Minimum Inhibitory Concentration (MIC) of chlorhexidine diacetate for E. coli ATCC 25922 (left) and S. aureus NCTC 12981 (right) determined by the reduction of resazurin to resorufin correlated to reduction in cellular viability (●). Error bars represent standard deviation, n = 8, **** p ≤ 0.0001.

Figure 8

Drug release trial of chlorhexidine diacetate (CHX): (a) determination of λmax, (b) standard curve, (c) 30-day real-time (■) and cumulative (☐) release of CHX from coated 10 mm samples, and (d) predicted 30-day CHX release from fully coated catheters (+CHX, △) and 50% coated catheters (+CHX50, ▽). Dashed line indicates the Minimum Inhibitory Concentration of CHX.