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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Struvite urolithiasis forms as a consequence of a urinary tract infection by urease-producing species of bacteria such as Proteus mirabilis. Ammonia, produced by the enzymatic hydrolysis of urea, elevates urine pH causing a supersaturation and precipitation of Mg++ as struvite (NH4MgPO4). Calcium often precipitates as well, forming the mineral carbonate-apatite (Ca10(PO4)6CO3). We have developed a procedure based on direct observation by light microscopy whereby struvite crystal growth can be quickly monitored in response to chemical changes in urine. As struvite crystals assume a characteristic shape or crystal habit based on their growth rate, the effect of urine chemistry and the action of various crystallization or urease inhibitors on struvite formation can be quickly shown. In addition preliminary effects of alkaline pH, or the presence of toxic compounds on bacteria can also be shown through their loss of motility.
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PMID:A simple technique for studying struvite crystal growth in vitro. 218 Jan 68

To compare the frequency of urine infection in calcium oxalate and calcium phosphate stone formers, we reviewed charts from patients whose last renal stone submitted for analysis was predominantly composed of calcium phosphate in 118 and of calcium oxalate in 223. Positive cultures were commoner, but not significantly, in the phosphate than the oxalate stone formers, both in men (17 vs. 7.6%) and women (22 vs. 15%). Bacteria frequently producing urease were found in only 4% of the phosphate group. Urine leucocytes were slightly more frequent in the oxalate group for men and significantly so for women. The results do not support the concept that calcium phosphate stones are mainly due to infection with urease-producing or other bacteria.
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PMID:Comparison of urinary tract infection in calcium oxalate and calcium phosphate stone formers. 220 21

Previous studies have shown human urine to have an inhibitory action on urease-induced crystallisation. Centrifugation and 0.45 microns filtration of the urine did not reduce this activity. This eliminates larger urine particles as being the cause of the inhibitory activity. Both the retenate and the filtrate after ultrafiltration of urine with a 100.000 mol weight cut-off influenced the urease-induced crystallisation of magnesium ammonium phosphate and calcium phosphate. The results indicate that the inhibitory action is exerted by more than one urinary component.
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PMID:The effects of fractioned human urine on urease-induced crystallisation in vitro. 231 71

The efficacy of a diet designed to facilitate dissolution of feline magnesium ammonium phosphate (struvite) uroliths was evaluated in 30 cases of urolithiasis, sterile struvite uroliths dissolved in a mean of 36 days after initiation of dietary treatment. In 5 cases of urolithiasis, struvite urocystoliths associated with urease-negative bacterial urinary tract infection dissolved in a mean of 23 days after initiation of dietary and antimicrobial treatment. In 3 cases of urolithiasis, struvite urocystoliths associated with urease-positive staphylococcal urinary tract infection dissolved in a mean of 79 days after initiation of dietary and antimicrobial treatment. Dissolution of uroliths in cats fed the treatment diet was associated with concomitant remission of dysuria, hematuria, and pyuria, and reduction in urine pH and struvite crystalluria. In one case, a urocystolith composed of 100% ammonium urate, and in another case, a urolith composed of 60% calcium phosphate, 20% calcium oxalate, and 20% magnesium ammonium phosphate did not dissolve.
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PMID:Medical dissolution of feline struvite urocystoliths. 232 73

Extensive cultures of stones and urine were performed in 215 patients who underwent an operation for upper urinary tract calculi. Microorganisms could be cultured from the stone in 1 of every 3 patients. Despite the extended culture technique urease-producing microorganisms could be cultured from the stone in only 48% of the patients with calculi that contained magnesium ammonium phosphate. This finding suggests that an infection with urease-producing microorganisms is not obligatory for the formation of this type of stone. Of the patients with calcium oxalate phosphate stones 32% had positive stone cultures, which distinguished them from patients with pure calcium oxalate stones, only 8% of whom had a positive stone culture (p less than 0.001).
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PMID:Bacteriology of upper urinary tract stones. 232 12

Struvite stones are formed as the result of urinary tract infection by urease-producing bacteria. Ultrastructural examination of calculi removed from a patient revealed bacteria incorporated throughout the stone matrix. Exopolysaccharide stained by ruthenium red was associated with most of the bacteria, but it represented only a small portion of the organic matrix in the stone. Localised deposits of calcium and phosphorus, components of carbonate-apatite, and magnesium, a struvite component, were detected in close proximity to the cells. Histochemical examinations revealed that several of the gram-negative bacteria within the stone matrix possessed high levels of urease activity. We propose that bacterial slime production, intimately involved in the initiation of stone matrix deposition, is less prominent in mature stones because of the increased incorporation of host-derived mucoproteins and mucopolysaccharides.
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PMID:Observations of the ultrastructure of infected kidney stones. 247 Sep 5

Zinc reduced and citrate promoted the urease-induced pH increase in synthetic urine. Secondary to this, the precipitation of magnesium ammonium phosphate and calcium phosphate was influenced. Independent of this pH-related effect, zinc also increased the precipitation of magnesium ammonium phosphate and decreased the calcium phosphate precipitation. These observations were not totally reproducable in human urine.
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PMID:The influence of zinc and citrate on urease-induced urine crystallisation. 274 46

Experimental and clinical studies have been performed to determine whether Ureaplasma urealyticum has an etiological role in the development of infection stones in the urinary tract. Incubation of synthetic urine in vitro with U. urealyticum caused alkalinization of the urine and crystallization of struvite and calcium phosphate. Inoculation of U. urealyticum into rat bladders resulted in the formation of struvite stones in 84% of the rats. Furthermore, infection with U. urealyticum markedly increased the adherence of urease-induced crystals to the bladder epithelium compared to normal rat bladders, probably due to elimination of the mucous coat which covers the normal urothelium. Clinically, U. urealyticum has been cultured from voided urine and from the stone in patients operated on for renal stones. U. urealyticum was cultured in voided urine in 31 of 247 patients (13%) with metabolic stones, compared to 43 of 145 patients (30%) with infection stones (p less than 0.001). In the patients where stone cultures were performed, U. urealyticum was found in 2 of 125 patients (2%) with metabolic stones, compared to 10 of 64 patients (16%) with infection stones (p less than 0.001). These observations strongly suggest that U. urealyticum is linked to the formation of infection stones in the urinary tract.
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PMID:Urinary infection stones caused by Ureaplasma urealyticum: a review. 304 57

Apart from urine supersaturation with respect to struvite and calcium phosphate, crystal retention is considered to be necessary for the formation of infection stones. This study was performed to investigate the role of the mucous coat in rat bladders in the adhesion of sterile urease-induced crystals and to determine to what extent the adhesion was influenced by infection. Elimination of the mucous coat with 0.1 M HCl increased the adherence of crystals six times compared to that in bladders with an intact mucous coat. Infection with Proteus mirabilis, Escherichia coli, enterococci and Ureaplasma urealyticum increased the adherence six, five, four and two times, respectively. Injury to the mucous coat may thus be one mechanism by which microorganisms can contribute to the formation of infection stones in the urinary tract.
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PMID:Adherence of urease-induced crystals to rat bladder epithelium following acute infection with different uropathogenic microorganisms. 329 48

Apart from urine supersaturation with respect to struvite and calcium phosphate caused by urease-producing microorganisms, retention of formed crystals in the urinary tract is necessary for the formation of infection stones. This study was performed to investigate the role of the mucous coat lining the urothelium in the adhesion of urease-induced crystals. Removal of this glycosaminoglycan-containing layer from rat bladders increased the adherence of struvite and calcium phosphate crystals 5-6 times compared to that in intact rat bladders. Heparin completely restored the antiadherence capacity while chondroitin sulphate had a very weak restorative effect and human urine had no restorative effect. These findings support the view that the mucous coat is of importance in preventing retention of urease-induced crystals.
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PMID:Adherence of urease-induced crystals to rat bladder epithelium. 334 64


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