Aj. Dumanski et al., UNIQUE ABILITY OF THE PROTEUS-MIRABILIS CAPSULE TO ENHANCE MINERAL GROWTH IN INFECTIOUS URINARY CALCULI, Infection and immunity, 62(7), 1994, pp. 2998-3003
Struvite (MgNH4PO4.6H(2)O) calculi are a common complication of Proteu
s mirabilis urinary tract infections. Although urease is a major virul
ence factor in calculus formation, the polysaccharide capsule (CPS) of
this organism also enhances struvite crystallization and growth in vi
tro (L. Clapham, R. J. C. McLean, J. C. Nickel, J. Downey, and J. W. C
osterton, J. Crystal Growth 104:475-484, 1990). We obtained purified C
PS, of known structure and varying anionic character, from P. mirabili
s ATCC 49565 and several other organisms. Artificial urine was added t
o CPS, and the pH was elevated from 5.8 to 8.5 by the addition of urea
se or titration with 0.25 4 NH2OH to induce struvite crystallization.
Crystallization was measured by particle counting (Coulter counter), a
nd the morphology (crystal habit) was examined by phase contrast micro
scopy. In the presence of partially anionic P. mirabilis CPS, struvite
formation occurred at a lower pH than in the absence of CPS pr in the
presence of other neutral, partially anionic, or anionic CPS. At pH 7
.5 to 8.0, significantly more struvite crystals formed in the presence
of P. mirabilis CPS than under other experimental conditions. With th
e exception of one polymer (curdlan) which did not bind Mg2+, enhancem
ent of struvite formation by CPS polymers was inversely proportional t
o their Mg2+ binding ability. We speculate that the structure and part
ial anionic nature of P. mirabilis ICPS enable it to enhance struvite
formation by weakly concentrating Mg2+ ions during struvite crystal fo
rmation. This illustrates a new virulence aspect of bacterial CPS duri
ng infection.