Iodinated non-ionic contrast medium does not inhibit Escherichia coli growth in ex vivo inoculated canine urine

To investigate the effect of iohexol on standardized quantitative urine culture results in dogs. The authors hypothesized that the presence of iohexol in inoculated urine samples would result in lower bacterial concentrations (CFU/mL) and, therefore, decrease culture sensitivity.

Urine samples were aseptically collected during cystoscopy from a single client-owned dog untreated with antimicrobials.

An experimental controlled study. The urine sample was divided into 38 aliquots (0.5 mL each) that were used as negative controls or inoculated with an equal amount of Escherichia coli (105 CFU/mL). Different volumes (0.1 and 0.5 mL) of contrast or saline were added to the aliquots and quantitative culture results were compared. Two different incubation times between the preparation of aliquots and culture were evaluated (15 minutes and 24 hours).

All aliquots from samples inoculated with E. coli (positive controls and iohexol-group) had the same reported quantitative result (104 CFU/mL). No growth was reported for the negative controls. Iohexol did not show any anti-E. coli properties in canine urine cultures for dilutions up to 1:2 contrast:urine and concentrations up to 120 mgI/mL. No difference was reported when iohexol was incubated with inoculated urine for 15 minutes or 24 hours.

Based on the experimental in vitro conditions described, administration of iohexol before the collection of urine during urologic procedures does not negatively impact the isolation and growth of E. coli.