Urease producing bacteria and staghorn calculi

Bacterial urease generates ammonia from urea, elevating the pH of urine (ie producing alkaline urine). Urinary tract pathogens that produce urease are called urea splitting or urea producing urinary bacteria:

• examples of urease producing (urea splitting) bacteria include Proteus mirabilis and some Klebsiella species
  
  
  • as the pH of urine rises, crystals of calcium and magnesium phosphates come out of solution
  • urease producing bacteria are associated with the incidence of staghorn calculi
    • staghorn calculi are upper urinary tract stones that involve the renal pelvis and extend into at least 2 calyces
      • all types of urinary stones can potentially form staghorn calculi but approximately 75% are composed of a struvite-carbonate-apatite matrix (so-called struvite stones)
      • two conditions must coexist for the formation of struvite calculi
        • alkaline urine (pH >7.2) and
        • the presence of ammonia in the urine
        • these two factors lead to magnesium ammonium phosphate and carbonate apatite crystallization

Urease - producing bacteria are also a concern because of the higher incidence of blocked urinary catheters that occur if there are urease- producing bacteria

• a study of the ability of 12 urease-positive species of urinary tract pathogens to encrust and block catheters was undertaken
  • Proteus mirabilis, Proteus vulgaris and Providencia rettgeri were able to raise the urinary pH above 8.3 and produce catheter-blocking crystalline biofilms within 40 h
    
    
  • Morganella morganii and Staphylococcus aureus elevated the pH of urine to 7.4 and 6.9, respectively, and caused some crystal deposition in the biofilms but did not block catheters in the 96 h experimental period
    
    
  • Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa and Providencia stuartii were only capable of raising the pH of urine to a maximum of 6.4 and failed to cause crystal deposition in the biofilm
    
    
  • most effective way to prevent catheter encrustation was shown to be diluting urine and increasing its citrate concentration
    • strategy raises the nucleation pH (pHn) at which calcium and magnesium phosphates crystallize from urine
    • increasing the fluid intake of a healthy volunteer with citrated drinks resulted in urine with a pHn of >8.0 in which catheter encrustation was inhibited

Reference:

• Broomfield RJ et al.Crystalline bacterial biofilm formation on urinary catheters by urease-producing urinary tract pathogens: a simple method of control. J Med Microbiol. 2009 Oct;58(Pt 10):1367-75.