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Infection and Immunity, July 2009, p. 2762-2772, Vol. 77, No. 7
0019-9567/09/$08.00+0     doi:10.1128/IAI.00323-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Urothelial Cultures Support Intracellular Bacterial Community Formation by Uropathogenic Escherichia coli{triangledown}

Ruth E. Berry, David J. Klumpp,* and Anthony J. Schaeffer

Department of Urology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, Illinois 60611

Received 20 March 2009/ Returned for modification 29 April 2009/ Accepted 4 May 2009

Uropathogenic Escherichia coli (UPEC) causes most community-acquired and nosocomial urinary tract infections (UTI). In a mouse model of UTI, UPEC invades superficial bladder cells and proliferates rapidly, forming biofilm-like structures called intracellular bacterial communities (IBCs). Using a gentamicin protection assay and fluorescence microscopy, we developed an in vitro model for studying UPEC proliferation within immortalized human urothelial cells. By pharmacologic manipulation of urothelial cells with the cholesterol-sequestering drug filipin, numbers of intracellular UPEC CFU increased 8 h and 24 h postinfection relative to untreated cultures. Enhanced UPEC intracellular proliferation required that the urothelial cells, but not the bacteria, be filipin treated prior to infection. However, neither UPEC frequency of invasion nor early intracellular trafficking events to a Lamp1-positive compartment were modulated by filipin. Upon inspection by fluorescence microscopy, cultures with enhanced UPEC intracellular proliferation exhibited large, dense bacterial aggregates within cells that resembled IBCs but were contained with Lamp1-positive vacuoles. While an isogenic fimH mutant was capable of forming these IBC-like structures, the mutant formed significantly fewer than wild-type UPEC. Similar to IBCs, expression of E. coli iron acquisition systems was upregulated by intracellular UPEC. Expression of other putative virulence factors, including hlyA, cnf1, fliC, kpsD, and the biofilm adhesin yfaL also increased, while expression of fimA decreased and that of flu did not change. These results indicate that UPEC differentially regulates virulence factors in the intracellular environment. Thus, immortalized urothelial cultures that recapitulate IBC formation in vitro represent a novel system for the molecular and biochemical characterization of the UPEC intracellular life cycle.

* Corresponding author. Mailing address: Department of Urology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611. Phone: (312) 908-1996. Fax: (312) 908-7275. E-mail: d-klumpp{at}northwestern.edu

{triangledown} Published ahead of print on 18 May 2009.

Editor: A. J. Bäumler

Infection and Immunity, July 2009, p. 2762-2772, Vol. 77, No. 7
0019-9567/09/$08.00+0     doi:10.1128/IAI.00323-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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