Tetrasodium EDTA for the prevention of urinary catheter infections and blockages

Abstract

Long-term catheterised individuals are at significant risk of developing catheter-associated urinary tract infections (CAUTIs), with up to 50% of patients experiencing recurrent episodes of catheter encrustation and blockage. Catheter blockage is a result of accumulation of carbonate apatite and struvite formed upon precipitation of ions within urine due to an infection-induced rise in pH. The aim of this study was to investigate the antimicrobial and anti-encrustation activities of tetrasodium ethylenediaminetetraacetic acid (tEDTA) to evaluate its potential efficacy in preventing CAUTIs and catheter blockages. The antimicrobial activity of tEDTA against uropathogens was assessed using time kill assays performed in artificial urine (AU). Crystallisation studies and in vitro bladder model assays were conducted to investigate the effect of tEDTA on struvite crystallisation and catheter blockage. tEDTA displayed bacteriostatic activity against Proteus mirabilis and prevented precipitation of ions in the AU. Crystallisation studies confirmed tEDTA inhibits struvite nucleation and growth via Mg²⁺ chelation with 7.63 mM tEDTA, equimolar to the concentration of divalent cations in AU, preventing the formation of crystalline deposits and blockage of Foley catheters for ≥168 h. The promising chelating abilities of low tEDTA concentrations could be exploited to inhibit encrustation and blockage of indwelling catheters. The fundamental research presented will inform our future development of an effective tEDTA-eluting catheter coating aimed at preventing catheter encrustation.

Fig. 1. Chemical structure of ethylenediaminetetraacetic acid tetrasodium salt hydrate (tEDTA).

Fig. 2. Schematic diagram of the in vitro bladder model assembly. A silicone 14 channel male Foley catheter was inserted into the bladder and held in place by inflating the balloon. The water bath supplied water at a temperature of 37 °C to the water jacket surrounding the inner chamber of the glass vessel. The peristaltic pump supplied sterile AU, stored in a 10 L sterile carboy, to the bladder at a rate of 0.75 mL min⁻¹. When the level of AU in the bladder reached the level of the catheter eyehole, the urine drained from the bladder and was collected in the attached urine collection bag.

Fig. 3. The pH (filled symbols) and viability (open symbols) of (a) S. aureus, (b) E. coli and (c) P. mirabilis-infected AU in the absence (control) and presence of tEDTA (7.63 or 28 mM). Error bars represent positive standard deviation (N = 3). Error bars not visible are less than the size of the symbols.

Fig. 4. Images of P. mirabilis-inoculated AU after 24 h incubation at 37 °C in an orbital incubator in the presence of (a) 7.63 mM tEDTA and (b) 0 mM tEDTA.

Fig. 5. Extent of reaction of struvite formation in the absence (control) and presence of 1, 3, 5, and 7 mM tEDTA. These are representative curves from three trials for each sample, where characteristic features (e.g. induction times and extent of reactions) are reproducible.

Fig. 6. Representative optical micrographs of the struvite crystals formed during bulk crystallisation studies in the (a) absence (control) and presence of (b) 1 mM, (c) 3 mM, (d) 5 mM, and (e) 7 mM tEDTA (N = 6). The inset is a scanning electron micrograph highlighting the elongated tabular habit of a representative struvite crystal. (f) Powder XRD patterns for the control and 7 mM tEDTA samples.

Fig. 7. (a) Reduction in growth rate of struvite crystals along three crystallographic directions as a function of tEDTA concentration. The growth solution consisted of 2.5 mM MgCl₂·H₂O/2.5 mM NH₄H₂PO₄/X mM tEDTA. (b) Time-elapsed optical micrographs demonstrated the effects of 1 mM tEDTA on struvite growth under solution flow (24 mL h⁻¹). Scale bar = 20 μm. Each data point represents the average measurements of 30 or more crystals in a single batch using the microfluidics platform. Error bars span two standard deviations. The lines are interpolations to guide the eye.

Fig. 8. (a) Images of catheters supplied with P. mirabilis-infected AU in the (i) absence and presence of (ii) 7.63 mM and (iii) 28 mM tEDTA, removed from the bladder model at (i) time of blockage (42 ± 5 h) or (ii and iii) at 168 h. (b) Time taken for catheters to block when supplied with P. mirabilis-infected AU in the absence and presence of tEDTA. Catheters exposed to tEDTA remained unblocked throughout the duration of the experiment (168 h). **** denotes significance (p ≤ 0.0001) and ‘ns’ represents no significant difference. (c) P. mirabilis viability and (d) pH of urine within the bladders at the start of the experiment, time of catheter blockage and at t = 168 h. Error bars represent positive single standard deviations of the mean values (N = 6).

Fig. 9. Representative scanning electron micrographs of catheter cross-sections directly below the catheter eyeholes. (a) A control catheter, supplied with AU without tEDTA, removed from the bladder model at the time of blockage (42 ± 5 h), with (b) displaying a magnified area of the deposits. Arrows have been added to highlight the struvite crystals present. Catheters supplied with AU containing (c) 7.63 mM tEDTA and (d) 28 mM tEDTA, removed from the bladder model at t = 168 h.