Proteus mirabilis viability after lithotripsy of struvite calculi

Urinary calculi composed of struvite harbor urease-producing bacteria within the stone. The photothermal mechanism of holmium:YAG lithotripsy is uniquely different than other lithotripsy devices. We postulated that bacterial viability of struvite calculi would be less for calculi fragmented with holmium:YAG irradiation compared to other lithotripsy devices. Human calculi of known struvite composition (greater than 90% magnesium ammonium phosphate hexahydrate) were incubated with Proteus mirabilis. Calculi were fragmented with no lithotripsy (controls), or shock wave, intracorporeal ultrasonic, electrohydraulic, pneumatic, holmium:YAG or pulsed dye laser lithotripsy. After lithotripsy, stone fragments were sonicated and specimens were serially plated for 48 hours at 38C. Bacterial counts and the rate of bacterial sterilization were compared. Median bacterial counts (colony forming units per ml) were 8×10 ⁶ in controls and 3×10 ⁶ in shock wave, 3×10 ⁷ in ultrasonic, 4×10 ⁵ in electrohydraulic, 8×10 ⁶ in pneumatic, 5×10 ⁴ in holmium:YAG and 1×10 ⁶ in pulsed dye laser lithotripsy, p<0.001. The rate of bacterial sterilization was 50% for holmium:YAG lithotripsy treated stones versus 0% for each of the other cohorts, p<0.01. P. mirabills viability is less after holmium:YAG irradiation compared to other lithotripsy devices.