Use of polymerase chain reaction to detect Proteus mirabilis and Ureaplasma urealyticum in urinary calculi

In this study, we evaluated the efficacy of the polymerase chain reaction ( PCR) in detecting urea-splitting microorganisms in desiccated urinary tract infection stones. Seventy-eight urinary tract stones were tested for the p resence of Proteus mirabilis and Ureaplasma urealyticum by means of PCR wit h species-specific primers. Twenty-seven stone samples were composed of str uvite and/or carbonate apatite (infection stone); 40 were calcium oxalate a nd/or calcium phosphate; seven were mixed, with struvite/carbonate apatite and calcium oxalate; and four were uric acid stones. PCR was performed with DNA extracted from pulverized stone pieces. Initial assays using the pulve rized stone specimens spiked with microorganisms showed that PCR could not detect U. urealyticum at densities below 10(3) color changing units (CCU), or P. mirabilis at densities below 10(4) colony-forming units (CFU). PCR wa s negative for U. urealyticum and P. mirabilis in all metabolic stones from patients. P. mirabilis was detected by PCR in 10 of 34 patients with infec tion stones. Preoperative urine cultures grew P. mirabilis in three of thes e 10 patients, and were negative for P. mirabilis in the other seven. U. ur ealyticum was detected by PCR in stone samples from four patients, two of w hich were also PCR-positive for P. mirabilis. All four of these patients ha d infection stones; two had residual stones, and the other two had recurren ce of urinary stones after their operations. These results demonstrate that microorganisms in urinary stones can be detected by PCR even when the void ed urine culture is negative. Investigations into the role of bacterial inf ection in stone formation will require further improvements in the sensitiv ity of PCR assays for pathogen detection.