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Regulation of P-Fimbrial Phase Variation Frequencies in Escherichia coli CFT073

Nicola Holden, Makrina Totsika, Lynn Dixon, Kirsteen Catherwood, and David L. Gally^*

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

Received 19 December 2006/ Returned for modification 12 March 2007/ Accepted 10 April 2007

Adherence of uropathogenic Escherichia coli 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 for 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 be different in E. coli CFT073 and E. coli K-12 as (i) phase variation could be stimulated in E. coli K-12 by induction of papI and (ii) the level of 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 that there is a hierarchy of expression depending on signal inputs.

Published ahead of print on 23 April 2007.

Editor: V. J. DiRita

N.H. and M.T. contributed equally to the work.