What is the pathogenesis of struvite stones in Proteus infections?

Updated: Mar 03, 2020
  • Author: Shirin A Mazumder, MD, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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The ability of Proteus organisms to produce urease and to alkalinize the urine by hydrolyzing urea to ammonia makes it effective in producing an environment in which it can survive. This leads to precipitation of organic and inorganic compounds, which leads to struvite stone formation. Struvite stones are composed of a combination of magnesium ammonium phosphate (struvite) and calcium carbonate-apatite.

Struvite stone formation can be sustained only when ammonia production is increased and the urine pH is elevated to decrease the solubility of phosphate. Both of these requirements can occur only when urine is infected with a urease-producing organism such as Proteus. Urease metabolizes urea into ammonia and carbon dioxide: Urea → 2NH3 + CO2. The ammonia/ammonium buffer pair has a pK of 9.0, resulting in the combination of highly alkaline urine rich in ammonia.

Symptoms attributable to struvite stones are uncommon. More often, women present with UTI, flank pain, or hematuria and are found to have a persistently alkaline urine pH (>7.0).

The acquisition of a particular phenotype known as "swarm cell differentiation" facilitates the ascent of P mirabilis into the urinary tract. The swarming behavior of Proteus species results in a characteristic bullseye pattern on a plate culture. When Proteus species swarm, the production of secreted proteins, including virulence factors such as the protease ZapA, dramatically increases,. This swarming motility is regulated through a complex network acting on the flagellar transcription regulator flhDC. The name Proteus follows from the character in Homer's Odyssey who is capable of changing form.

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