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Infection and Immunity, May 2001, p. 2838-2846, Vol. 69, No. 5
Department of Microbiology and
Immunology1 and Division of Infectious
Diseases,2 University of Maryland School of
Medicine, and Department of Veterans
Affairs,3 Baltimore, Maryland 21201
Received 6 October 2000/Returned for modification 27 November
2000/Accepted 22 January 2001
Escherichia coli is the primary cause of uncomplicated
infections of the urinary tract including cystitis. More serious
infections, characterized as acute pyelonephritis, can also develop.
Type 1 fimbriae of E. coli contribute to virulence in the
urinary tract; however, only recently has the expression of the type 1 fimbriae been investigated in vivo using molecular techniques.
Transcription of type 1 fimbrial genes is controlled by a promoter that
resides on a 314-bp invertible element capable of two orientations. One places the promoter in the ON orientation, allowing for transcription; the other places the promoter in the OFF orientation, preventing transcription. A PCR-based assay was developed to measure the orientation of the invertible element during an experimental urinary tract infection in mice. Using this assay, it was found that the percentage of the population ON in urine samples correlated with the
respective CFU per gram of bladder (P = 0.0006) but
not with CFU per gram of kidney (P > 0.069). Cystitis
isolates present in the urine of mice during the course of infection
had a higher percentage of their invertible elements in the ON
orientation than did pyelonephritis isolates (85 and 34%,
respectively, at 24 h; P < 0.0001). In general,
cystitis isolates, unlike pyelonephritis isolates, were more likely to
maintain their invertible elements in the ON orientation for the entire
period of infection. E. coli cells expressing type 1 fimbriae, expelled in urine, were shown by scanning electron microscopy
to be densely packed on the surface of uroepithelial cells. These
results suggest that expression of type 1 fimbriae is more critical for
cystitis strains than for pyelonephritis strains in the early stages of
an infection during bladder colonization.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.5.2838-2846.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
In Vivo Dynamics of Type 1 Fimbria Regulation in Uropathogenic
Escherichia coli during Experimental 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) 706-6751. E-mail: hmobley{at}umaryland.edu.
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