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Infect. Immun. doi:10.1128/IAI.01989-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Regulation of P-fimbrial phase variation frequencies in Escherichia coli CFT073

Centre for Infectious Diseases, Royal (Dick) School of Veterinary Studies, Chancellor's Building, University of Edinburgh, Edinburgh, EH16 4SB, United Kingdom

^* To whom correspondence should be addressed. Email: dgally{at}ed.ac.uk.

	Abstract

Adherence of uropathogenic Escherichia coli (UPEC) to host tissue is required for infection and is mediated by fimbriae, such as pyelonephritis-associated pili (Pap). Expression of P-fimbriae is regulated by phase variation and to date, phase transition frequencies have been measured only for pap regulatory region constructs integrated into the E. coli K-12 chromosome. The aim of this work was to measure P phase transition frequencies in clinical isolates for the first time, including frequencies for the sequenced strain E. coli CFT073. P-fimbriation and associated phase transition frequencies were measured in two E. coli clinical isolates and compared with levels for homologous pap constructs in E. coli K-12. Fimbriation and off-to-on transition frequencies were always higher in the clinical isolate. It was concluded that the regulatory inputs controlling papI expression are likely to differ between E. coli CFT073 and E. coli K-12 as: (1) phase variation could be stimulated in E. coli K-12 by induction of papI and (2) expression of a papI::gfp⁺ fusion was higher in E. coli CFT073 than in E. coli K-12. Furthermore phase transition frequencies for the two E. coli CFT073 pap clusters were shown to be different depending on the culture conditions, indicating a hierarchy of expression depending on signal inputs.