Why uti &bacteriia can lead renal calculi?

Struvite stones.: The only causative link between UTI and kidney stones is in the formation of struvite, or magnesium ammonium phosphate, stones. These stones form when there is high ammonium phosphate and high urine ph. The only situation in which this occurs in humans is with a urinary tract infection with a urease-producing organism, such as proteus or klebsiella, which breaks down urine urea into ammonia.

Proteus mirabilis: Infection with the bacteria proteus mirabilis can cause a more alkaline urine, which can increase the risk of kidney stone formation. The bacteria can then "hide" in the stones, so that the infection recurs after antibacterial treatment.