Calcium phosphate crystal formation in Escherichia coli from human urine: an in vitro study

Escherichia coli with no demonstrable urease activity was inoculated into filter sterilized urine obtained from a healthy volunteer subject with no history of stone disease and then incubated at 37 degrees C. Bacteria were recovered at intervals between 1 and 10 days. Urinary pH was stable as compared to control urines and spontaneous crystal precipitation was not noted in controls. Recovered organisms were analyzed by x-ray powder diffractometry. An uncharacterized mineral phase (UMP) was first evident after 6 days. Calcium phosphate in the form of brushite and hydroxyapatite was apparent at 7 and 10 days respectively. This suggests a role for bacteria in calcium phosphate crystal formation in urine apart from urease activity and may contribute to the calcium phosphate component of urinary calculi.