Quantification of Proteus mirabilis virulence factors and modulation by acylated homoserine lactones.

Background and Purpose: Measurement of the main Proteus mirabilis virulence factors would increase our understanding of how the organism infects and colonizes the urinary tract. The purpose of this study was to quantify the virulence factors of twelve P. mirabilis laboratory strains and to determine whether expression of virulence factors of P. mirabilis depends on the presence of homoserine-lactone derivatives. Methods: Twelve P. mirabilis strains with defined lipopolysaccharide structures were used. The activity levels of urease, proteases, and hemolysins and the swarming abilities of P. mirabilis rods were tested by qualitative and quantitative methods. The effect of addition of acylated homoserine lactones (acyl-HSLs) was evaluated in order to determine their influence on the pathogenic features of the P. mirabilis strains. Results: The ureolytic, proteolytic, and hemolytic abilities and the swarming motility of P. mirabilis rods were strain-specific. The P. mirabilis strains which possessed a negatively charged O-polysaccharide demonstrated strong ureolytic and proteolytic properties and faster migration speed on solid media. There was no influence of acyl-HSLs on the process of urea decomposition. The acyl-HSLs inhibited the protease activity of five P. mirabilis strains. N-butanoyl-L-homoserine lactone accelerated the migration speed of the tested P. mirabilis strains. Conclusions: The levels of tested virulence factors were strain-specific. The acetylated homoserine lactone derivatives modified the expression of some virulence factors of the P. mirabilis strains.