CONSTRUCTION OF AN MR P FIMBRIAL MUTANT OF PROTEUS-MIRABILIS - ROLE IN VIRULENCE IN A MOUSE MODEL OF ASCENDING URINARY-TRACT INFECTION/

Proteus mirabilis, a cause of acute pyelonephritis, produces at least four types of fimbriae, including MR/P (mannose-resistant/Proteus-like ) fimbriae. To investigate the contribution of MR/P fimbriae to coloni zation of the urinary tract, we constructed an MR/P fimbrial mutant by allelic exchange. A 4.2-kb BamHI fragment carrying the mrpA gene was subcloned into a mobilizable plasmid, pSUP202. A 1.3-kb Kan(r) cassett e was inserted into the mrpA open reading frame, and the construct was transferred to the parent P. mirabilis strain by conjugation. Followi ng passage on nonselective medium, 1 of 500 transconjugants screened w as found to have undergone allelic exchange as demonstrated by Souther n blot. Colony immunoblot, Western immunoblot, and immunogold labeling with a monoclonal antibody to MR/P fimbriae revealed that MrpA was no t expressed. Complementation with cloned mrpA restored MR/P expression as shown by hemagglutination, Western blot, and immunogold electron m icroscopy. To assess virulence, we challenged 40 CBA mice transurethra lly with 10(7) CFU of wild-type or mutant strains. After 1 week, geome tric means of log(10) CFU per milliliter of urine or per gram of bladd er or kidney for the wild-type and mutant strains were as follows: uri ne, 7.79 (wild type) versus 7.02 (mutant) (P = 0.035); bladder, 6.22 v ersus 4.78 (P = 0.019); left kidney, 5.02 versus 3.31 (P = 0.009); and right kidney, 5.28 versus 4.46 (P = 0.039). Mice challenged with the wild-type strain showed significantly more severe renal damage than di d mice challenged with the MR/P-negative mutant (P = 0.007). We conclu de that MR/P fimbriae contribute significantly to colonization of the urinary tract and increase the risk of development of acute pyelonephr itis.