BACTERIOLOGY OF URINARY-TRACT STONES

It has been reported that up to half of renal stones and associated ur ine specimens have been positive on culture, and that up to 50% of suc h stones contain magnesium ammonium phosphate. In a prospective study using infrared and wet chemical analysis, we found positive cultures i n only 7 of 132 renal, 5 of 105 ureteral and 6 of 21 bladder stones ob tained surgically and handled with sterility. Of the culture positive calculi only 43% from the kidney, none from the ureter and 50% from th e bladder contained detectable magnesium ammonium phosphate. However, magnesium ammonium phosphate was detectable in 20% of renal, 2% of ure teral and 27% of bladder stones with negative cultures. Of the culture positive renal and ureteral calculi 42% were predominantly calcium ph osphate and 17% were predominantly calcium oxalate. For culture negati ve stones 25% and 51% from the kidney, and 15% and 82% from the ureter were composed of predominantly calcium phosphate and calcium oxalate, respectively. Among the culture positive stones, related positive uri ne cultures were noted in 100% of the renal, 20% of the ureteral and 5 0% of the bladder cases, compared to 26%, 10% and 27%, respectively, o f culture negative calculi. The same organism was found in the stone a nd urine in only 38% of the cases. The lower frequency of positive uri ne cultures, of stones with magnesium ammonium phosphate, and especial ly of culture positive renal and ureteral stones (5%) than in previous reports suggests that stone culture may be of less value than indicat ed previously, except for bladder calculi and large renal stones, such as the branched type.