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Proteus mirabilis biofilm protection against struvite crystal dissolution and its implications in struvite
R J McLean1, J R Lawrence, D R Korber
1Department of Urology, Queen's University, Kingston, Ontario, Canada.
Abstract:
Proteus mirabilis biofilm formation, struvite (MgNH4PO4.6H2O) crystal formation and dissolution in an artificial urine mixture were monitored using computer-enhanced microscopy (CEM) and a 1 x 3 mm. glass flow cell. Image analysis showed that P. mirabilis biofilm formation did not occur to any extent at macroenvironment flow rates greater than two mL/h (equivalent to a microenvironment flow rate of less than 5 microns./sec). Essentially, cells attached to glass surfaces, grew slowly and divided. Daughter cells were generally released directly into the medium where they could then presumably colonize other regions. Microcolonies formed by the adhesion of aggregates of cells from the medium, and over time grew into biofilms. Struvite crystallization due to urease activity and pH elevation above neutrality, was preceded by the deposition of organic matter on the glass surface, followed by the appearance of a number of tiny (one to two microns.) crystals. Crystals forming within a biofilm at low dilution rates took on a characteristic twinned or "X-shaped" appearance (crystal habit) indicative of a rapid growth rate. Those forming outside the biofilm took on a more tabular appearance reflecting their slower growth. When the macroenvironment flow rate of artificial urine (initial pH 5.8) in the glass flow cell was increased from two mL/h to four mL/h, struvite crystals not associated with biofilms dissolved within five to 10 min. Crystals entrapped within the P. mirabilis biofilm withstood flow rates up to 200 mL/h presumably due to the maintenance of an alkaline Mg-saturated microenvironment within the biofilm. These observations may suggest a mechanism by which struvite calculi can grow in spite of neutral or acidic urine pH and resist mild acidification therapy.
Insights
Proteus mirabilis biofilms protect struvite crystals from dissolution by maintaining an alkaline microenvironment. This suggests a mechanism for stone growth and resistance to acidification therapy.
Area of Science:
- Microbiology
- Biomineralization
- Urology
Background:
- Proteus mirabilis is a key pathogen in urinary tract infections, known for urease production.
- Urease activity leads to ammonia production, increasing urine pH and promoting struvite crystal formation.
- Biofilm formation by P. mirabilis can influence the urinary environment and stone development.
Purpose of the Study:
- To investigate the interplay between P. mirabilis biofilm formation and struvite crystal dynamics.
- To understand how biofilm structure affects crystal dissolution under varying flow conditions.
- To elucidate potential mechanisms of struvite calculus formation and resistance to therapy.
Main Methods:
- Computer-enhanced microscopy (CEM) was used to monitor biofilm and crystal formation in an artificial urine mixture.
- Experiments were conducted in a glass flow cell with controlled macroenvironment flow rates.
- Image analysis quantified biofilm development and crystal morphology and dissolution.
Main Results:
- P. mirabilis biofilm formation was inhibited at flow rates above 2 mL/h.
- Struvite crystallization occurred on organic matter, with crystals inside biofilms exhibiting an 'X-shaped' habit.
- Crystals within biofilms resisted dissolution at high flow rates (up to 200 mL/h), unlike those outside biofilms.
Conclusions:
- P. mirabilis biofilms create a protective microenvironment that promotes struvite crystal stability.
- The biofilm's alkaline, Mg-saturated microenvironment facilitates struvite calculus growth and resilience.
- These findings offer insights into urinary stone pathogenesis and potential therapeutic strategies.