Whole-cell Proteus mirabilis urease inhibition by aminophosphinates for the control of struvite formation

The study evaluated the in vitro impact of a series of aminophosphinic urease inhibitors on Proteusmirabilis. The group of compounds comprised structurally diverse analogues of diamidophosphate built on an N-C-P scaffold. The influence of urease inhibition on urea-splitting activity was assessed by whole-cell pH-static kinetic measurements. The potential to prevent struvite formation was determined by monitoring changes in pH and ionic composition of artificial urine medium during P. mirabilis growth. The most active compounds exhibited stronger positive effect on urine stability than the acknowledged inhibitor acetohydroxamic acid. The high anti-ureolytic and pH-stabilizing effect of urease inhibitors 4 and 14 was well correlated with their reported kinetic properties against pure urease from P. mirabilis (Ki values of 0.62±0.09 and 0.202±0.057 µM, respectively, compared to 5.7±0.4 µM for acetohydroxamic acid). The effect of repressed ureolysis upon the viability of Proteus cells was studied using MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide] metabolic efficiency assay and LIVE/DEAD fluorescent staining. Most of the compounds caused whole-cell dehydrogenase activity loss; four structures (1, 2, 4 and 14) reduced the culture viability by nearly 70 % at 1 mM concentration. Results of dual fluorescent staining suggested that besides urea-splitting prevention, the structures additionally exerted an outer-membrane-destabilizing effect.