Identification of MrpI as the sole recombinase that regulates the phase variation of MR/P fimbria, a bladder colonization factor of uropathogenic Proteus mirabilis

Mol Microbiol. 2002 Aug;45(3):865-74. doi: 10.1046/j.1365-2958.2002.03067.x.


Proteus mirabilis is a common cause of urinary tract infection (UTI) in individuals with structural abnormalities or long-term catheterization. The expression of mannose-resistant/Proteus-like (MR/P) fimbria is phase variable because of the inversion of a 251 bp DNA fragment that carries the promoter for the mrp operon. Previous studies have shown that mrpI, which is transcribed divergently from the mrp operon, encodes a recombinase capable of switching the orientation of this invertible element. In this study, we constructed isogenic mrpI null mutants from a clinical isolate of P. mirabilis, HI4320. A polymerase chain reaction (PCR)-based invertible element assay revealed that the isogenic mrpI null mutants were locked in one phase, either expressing (locked on) MR/P fimbriae or not (locked off), which indicated that MrpI was the sole recombinase that regulated the phase variation of MR/P fimbria. The locked-on and locked-off mutants were evaluated for virulence in the CBA mouse model of ascending UTI by co-challenges with each other and with the wild-type strain. Results from these experiments demonstrated conclusively that the MR/P fimbria was a critical bladder colonization factor of uropathogenic P. mirabilis and also suggested that the ability to switch off the expression of MR/P fimbria might be important for kidney colonization.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Bacterial Proteins
  • DNA Nucleotidyltransferases / physiology*
  • Fimbriae, Bacterial / genetics
  • Fimbriae, Bacterial / metabolism*
  • Gene Expression Regulation, Bacterial
  • Genetic Complementation Test
  • Kidney / microbiology
  • Mannose / metabolism*
  • Mice
  • Mice, Inbred CBA
  • Models, Animal
  • Molecular Sequence Data
  • Polymerase Chain Reaction
  • Proteus Infections / metabolism*
  • Proteus Infections / microbiology
  • Proteus mirabilis / genetics
  • Proteus mirabilis / pathogenicity
  • Proteus mirabilis / physiology*
  • Recombinases
  • Urinary Bladder / microbiology


  • Bacterial Proteins
  • Recombinases
  • mrpA protein, Proteus mirabilis
  • DNA Nucleotidyltransferases
  • Mannose

Associated data

  • GENBANK/Z32686