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Infection and Immunity, June 1999, p. 2822-2833, Vol. 67, No. 6
Department of Microbiology and Immunology,
University of Maryland, Baltimore, Maryland 21201
Received 28 September 1998/Returned for modification 4 December
1998/Accepted 18 March 1999
Two new genes, mrpH and mrpJ, were
identified downstream of mrpG in the mrp gene
cluster encoding mannose-resistant Proteus-like (MR/P)
fimbriae of uropathogenic Proteus mirabilis. Since the predicted MrpH has 30% amino acid sequence identity to PapG, the Gal
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Requirement of MrpH for Mannose-Resistant
Proteus-Like Fimbria-Mediated Hemagglutination by
Proteus mirabilis
(1-4)Gal-binding adhesin of Escherichia coli P
fimbriae, we hypothesized that mrpH encodes the functional
MR/P hemagglutinin. MR/P fimbriae, expressed in E. coli
DH5
, conferred on bacteria both the ability to cause
mannose-resistant hemagglutination and the ability to aggregate to form
pellicles on the broth surface. Both a
mrpH mutant
expressed in E. coli DH5
and an isogenic mrpH::aphA mutant of P. mirabilis were unable to produce normal MR/P fimbriae
efficiently, suggesting that MrpH was involved in fimbrial assembly.
Amino acid residue substitution of the N-terminal cysteine residues
(C66S and C128S) of MrpH abolished the receptor-binding activity
(hemagglutinating ability) of MrpH but allowed normal fimbrial
assembly, supporting the notion that MrpH was the functional MR/P
hemagglutinin. Immunogold electron microscopy of P. mirabilis HI4320 revealed that MrpH was located at the tip of
MR/P fimbriae, also consistent with its role in receptor binding. The
isogenic mrpH::aphA mutant of HI4320
was less able to colonize the urine, bladder, and kidneys in a mouse
model of ascending urinary tract infection (P < 0.01), and therefore MR/P fimbriae contribute significantly to
bacterial colonization in mice. While there are similarities between
P. mirabilis MR/P and E. coli P fimbriae, there
are more notable differences: (i) synthesis of the MrpH adhesin is
required to initiate fimbrial assembly, (ii) MR/P fimbriae confer an
aggregation phenotype, (iii) site-directed mutation of specific
residues can abolish receptor binding but allows fimbrial assembly, and
(iv) mutation of the adhesin gene abolishes virulence in a mouse model of ascending urinary tract infection.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201. Phone: (410) 706-0466. Fax:
(410) 706-2129. E-mail: hmobley{at}umaryland.edu.
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