Regulation of Urease Levels in Microcosm Dental Plaque

Abstract

The regulation of plaque urease activity by urea, ammonia and arginine was examined using microcosm dental plaques cultured in a multi-plaque 'artificial mouth' from the mixed oral microbiota. The plaques were supplied periodically with sucrose and continuously (3.6 ml/h/plaque) with a mucin containing medium (BMM) supplemented either with urea at concentrations found in saliva, or with arginine, or ammonia. Urease levels in plaque range from 400 to 1500 nmol NH₃/min/mg plaque protein. In the absence of urea supplementation, microcosm plaque urease levels were usually less than 100 nmol NH₃/min/mg protein. They decreased after 2 to 3 wks growth and were not restored by subsequent urea application. BMM containing 1, 5 and 20 mmol/l urea throughout growth produced a proportional increase in urease levels initially, similar to those observed in plaques in vivo. Subsequently, urease levels decreased as the plaques aged. BMM supplemented with arginine (1 mmol/l) or ammonia (2 mmol/l) reduced urease levels. The high urease levels found in supragingival plaque can be explained by the availability of urea at concentrations secreted in saliva. Ammonia and arginine lowered plaque urease levels.

Key Words:

• microcosm plaque
• plaque urease
• urea
• ammonia
• arginine