What bacteria that produce urease (an enzyme) cause the formation of struvite stones?

From the Guidelines

Struvite stones are primarily caused by urease-producing bacteria that infect the urinary tract, with the most common bacteria responsible being Proteus mirabilis, though others include Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and some Enterococcus species. These bacteria produce the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide, raising urine pH and creating an alkaline environment that promotes the crystallization of magnesium ammonium phosphate (struvite) and calcium phosphate 1.

Key Points

• The formation of struvite stones is strongly associated with urinary tract infections caused by specific organisms that produce the enzyme urease, such as Proteus mirabilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and some Enterococcus species 1.
• Treatment typically involves complete surgical removal of the stone (percutaneous nephrolithotomy or open surgery for larger stones) combined with appropriate antibiotics based on urine culture results, with common antibiotics including fluoroquinolones, trimethoprim-sulfamethoxazole, or aminoglycosides for 1-2 weeks, though longer courses may be needed for complicated infections.
• Prevention strategies include treating urinary tract infections promptly, maintaining adequate hydration, and in recurrent cases, considering urease inhibitors like acetohydroxamic acid.
• Patients with neurogenic bladders, indwelling catheters, or urinary diversions are at higher risk for developing these stones due to increased susceptibility to urinary tract infections with urease-producing organisms.

Management

• Clinicians should monitor patients with struvite stones for reinfection 1.
• Complete removal of the stone is an important goal in order to eradicate any causative organisms, relieve obstruction, prevent further stone growth and any associated infection, and preserve kidney function 1.
• The AUA Nephrolithiasis Guideline Panel believes that complete stone removal should remain a therapeutic goal, especially when a struvite/calcium carbonate/apatite stone is present 1.

From the Research

Bacteria Causing Struvite Stones

• The formation of struvite stones is caused by bacteria that produce urease, an enzyme that splits urea into ammonia and carbon dioxide, leading to urine alkalinization and the formation of phosphate salts 2, 3, 4, 5.
• Proteus species are the primary urease-producers responsible for struvite stone formation, although other Gram-negative and Gram-positive species may also produce urease 2, 3, 4, 5.
• Other urease-producers that can cause struvite stones include Ureaplasma urealyticum and Corynebacterium urealyticum, which require specific tests for identification 2.

Treatment and Prevention

• Treatment of struvite stones typically involves surgical removal of the stones, followed by antibiotic therapy to treat the underlying infection 2, 3, 4, 5.
• Urease inhibitors and acidification therapy may also be used to prevent recurrence of struvite stones 2, 3, 6, 4.
• Citrate salts may be administered to increase the nucleation pH and reduce the risk of struvite crystallization 2.