From bacteria to the urinary stone - on the growth of crystals induced by bacteria

Jolanta Prywer Institute of Physics, Lodz University of Technology, Wólczańska 219, Łódź

A separate group of urinary stones are the so-called Infectious stones formed as a result of infection of the urinary tract with appropriate microorganisms. Usually these are microorganisms of the Proteus species producing urease - a bacterial enzyme that breaks down urea, (NH2)2CO, physiologically present in the urine of a healthy person, to the final products: carbon dioxide, CO2, and ammonia, NH3. The bacterial-induced decomposition of urea initiates a cascade of chemical reactions that consequently lead to an increase in urine pH and crystallization of struvite, carbonate apatite (CA) and hydroxyapatite (HAP). These solid phases aggregate with each other as well as with bacteria and with the exfoliating cells of the urinary tract epithelium forming an infectious urinary stone. Bacteria not only initiate nucleation by decomposing urea, but also actively participate in the processes of growth of these solid phases affecting the structure of the surface of the crystal faces and the structure of the volume of crystals causing their porosity (Fig. 1), which is a unique feature of crystallization in the presence of microorganisms. The porosity produced by the bacteria increases the adhesion of the bacteria to the crystals, which hinders the leaching of bacteria from the urinary tract and enhances the formation of stone.

Left: a struvite crystal with a porous structure caused by bacteria present in the urine in which the crystal was growing; clusters of CA and HAP (green) and bacteria (blue) can be seen on the crystal [1]. Right: a struvite crystal growing (a) in the presence of microorganisms of Proteus species [1]; (b) without the presence of microorganisms [2]. Scale: 10 m. Bacteria, in particular dead are active centres of heterogeneous nucleation; they also affect the shape of the crystals formed. In the presence of bacteria, the crystals show a more regular habit. In addition, the presence of bacteria in urine promotes solid phases aggregation. Most of the processes listed above are explained by electrostatic interactions. It is known that microorganisms, or rather their outermost cells, contain negatively charged residues, mainly lipopolysaccharides. This means that lipopolysaccharides are capable of electrostatic interactions, in particular they can attract positive ions. In this way, microorganisms create a microenvironment different in concentration of Ca2+ and Mg2+ ions, which affects the physicochemical processes occurring in the urine. This means that microorganisms actively mediate the processes of crystal growth. Bibliography:

1. J. PRYWER, A. TORZEWSKA, CRYST. RES. TECHNOL. 45 (2010) NR 12, 1283–1289. 2. J. PRYWER, A. TORZEWSKA, T. PŁOCIŃSKI, UROL. RES., 40 (2012) NR 6, 699–707.

Keywords: biocrystallization, biomineralization, crystal growth, biogenic crystals