New aspects of the role of MR/P fimbriae in Proteus mirabilis urinary tract infection.

Proteus mirabilis, a common cause of urinary tract infection (UTI), produces a number of different fimbriae including mannose-resistant Proteus-like fimbriae (MR/P). The precise role of different P. mirabilis fimbriae in ascending UTI has not yet been elucidated. In this study, a clinical isolate of P. mirabilis and an isogenic mutant unable to express MR/P were tested using different experimental approaches. They were tested for their ability to cause infection in an ascending co-infection model of UTI and in a haematogenous model in the mouse. In both models, the mutant was less able than the wild-type strain to colonise the lower and upper urinary tracts although infectivity was not abolished. In vitro adherence to uroepithelial cells was also assessed. Significant differences in adherence between both strains were observed at 1 h but not at 15 min post infection. We have also shown that a wild-type strain carries two copies of the mrpA gene. These data reinforce the importance of MR/P fimbriae in P. mirabilis UTI although other virulence factors may be necessary for efficient colonisation and development of infection.

Virulence of a Proteus mirabilis ATF isogenic mutant is not impaired in a mouse model of ascending urinary tract infection.

Proteus mirabilis, a common cause of urinary tract infection, produces a number of different fimbriae, including ambient temperature fimbriae (ATF). These fimbriae are optimally expressed at 23 degrees C and their contribution to urinary tract infection has so far remained unknown. In the present study, a clinical isolate of P. mirabilis and an isogenic allelic replacement mutant unable to express ATF were tested for their ability to cause infection in the ascending urinary tract infection model in mice. The atf mutant colonised the urinary tract as well as the wild-type strain and was also able to outcompete the wild-type strain in a co-challenge experiment. Different non-clinical P. mirabilis isolates showed a reactive AtfA band after Western blot analysis using a polyclonal rabbit AtfA antiserum. These data together suggest that ATF does not play a role in P. mirabilis urinary tract infection.

Proteus mirabilis mannose-resistant, Proteus-like fimbriae: MrpG is located at the fimbrial tip and is required for fimbrial assembly.

The mannose-resistant, Proteus-like (MR/P) fimbria, responsible for mannose-resistant hemagglutination, is a virulence factor for uropathogenic Proteus mirabilis. Based on known fimbrial gene organization, we postulated that MrpG, a putative minor subunit of the MR/P fimbria, functions as an adhesin responsible for hemagglutination, while MrpA serves as the major structural subunit for the filamentous structure. To test this hypothesis, an mrpG mutant was constructed by allelic-exchange mutagenesis and verified by PCR and Southern blotting. The mrpG mutant was found to be negative for hemagglutination, while wild-type strain H14320 and the complemented mutant were positive. Western blots with antiserum raised against an overexpressed MrpG'-His6 fusion protein showed that MrpG was present in the fimbrial preparations of both the wild-type strain and the complemented mutant but absent in that of the mrpG mutant. The mrpG mutant was significantly less virulent in a CBA mouse model of ascending urinary tract infection. Western blots with antiserum to whole MR/P fimbriae showed that MrpA protein was also missing from the fimbrial preparation of the mrpG mutant. Using immunogold electron microscopy, we found that the normal MR/P-fimbrial structure was absent in the mrpG mutant, suggesting that MrpG is essential for initiation of normal fimbrial formation. In the wild-type strain, MrpG protein was localized to the tips of the fimbriae or at the surface of the cell when antiserum raised against overexpressed MrpG was used. Given the tip localization, MrpG may be required for initiation of assembly of MR/P fimbriae but does not appear to be the fimbrial adhesin.