Downloaded from www.microbiologyresearch.org by IP: 54.157.13.203 On: Fri, 05 Feb 2016 23:07:26 Microbiology (2001), 147, 145–152 Printed in Great Britain Analysis of type 1 fimbriae expression in verotoxigenic Escherichia coli : a comparison between serotypes O157 and O26 Andrew J. Roe, Carol Currie, David G. E. Smith and David L. Gally Author for correspondence : David Gally. Tel : 44 131 651 1342. Fax: 44 131 650 6531. e-mail : d.gallyed.ac.uk Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, Teviot Place, University of Edinburgh, Edinburgh EH8 9AG, UK Previous research has shown that verotoxin-producing Escherichia coli (VTEC) O157 strains appear unable to express type 1 fimbriae although other serotypes such as O26 and O118 can. This study has investigated the molecular basis of this difference. The study confirmed the presence of a 16 bp deletion within the regulatory region of fimA (fim switch) in 63 VTEC O157 strains but not in other VTEC serotypes tested. The fim switch was shown to be detectable only in the phase off orientation in VTEC O157, but detection of the switch in the phase on orientation correlated with the degree of mannose-sensitive yeast agglutination in VTEC O26. Repair of the 16 bp deletion in the VTEC O157 fim switch region restored phase-variable expression of fimA in a permissive background. Non-O157 VTEC, especially O26 and O118, can be pathogenic in cattle ; the role of type 1 fimbriae in this and colonization is discussed. Keywords : Escherichia coli O157, VTEC, type 1 fimbriae, phase variation, adherence INTRODUCTION Ruminants, particularly cattle, act as the main reservoir for verotoxigenic Escherichia coli (VTEC) (Beutin, 1999 ; Borczyk et al., 1987; Chart, 1998; Mead & Griffin, 1998 ; Ørskov et al., 1987). E. coli O157 is the most common serotype associated with VTEC infections in the UK and the USA, other serotypes such as O26 and O118 being prevalent in other countries (Beutin, 1999 ; Mead & Griffin, 1998). Except in the case of neonatal cattle (DeanNystrom et al., 1997), VTEC O157 does not cause disease in the bovine host, but diarrhoea and haemorrhagic colitis have been associated with other VTEC serotypes, especially O26 (Pearson et al., 1999 ; Stordeur et al., 2000). The very fact that VTEC O157 does not cause disease in ruminants may have helped its successful spread to 20–30 % of herds in England and Scotland as well as 40–70 % of herds in the USA in recent years (Elder et al., 2000; Gansheroff & O’Brien, 2000 ; Synge, 1999, 2000). In humans, the serious sequelae of haemorrhagic colitis and haemolytic uraemic syndrome stem from the ................................................................................................................................................. Abbreviations : A/E, attaching and effacing ; IHF, integration host factor ; VTEC, verotoxigenic E. coli. activity of the shiga-like toxins, and include gastro- intestinal tract colonization and damage involving intimate attachment and attaching and effacing (AE) lesion formation (Frankel et al., 1998 ; Kaper, 1998). Intimin is the key candidate initiating bacterial binding (DeVinney et al., 1999 ; Kenny, 1999) in the human host, possibly at the Peyer’s patches of the small intestine (Phillips & Frankel, 2000). There is a great deal of interest in understanding the successful dissemination of VTEC O157 among beef and dairy cattle and the reasons why it does not cause colitis and diarrheoa in this host. A logical starting point for such investigations is the carriage and expression of established bacterial adhesins, although to date there is no clear evidence that E. coli O157 colonizes the bovine gastrointestinal tract by binding to the epithelium. E. coli O157 does not carry genes for many of the established adhesins that could play a role in colonizing the bovine host, such as K99 and F41 (our unpublished data), but it does carry the genes for type 1 fimbriae. Type 1 fimbriae are the most common adhesin produced by E. coli and mediate adherence to mannose-containing glycoproteins found on the surfaces of many eukaryotic cells. Type 1 fimbriae have been shown to play an important role in the colonization of E. coli in the human urinary tract (Connell et al., 1996 ; Donnenberg & Welch, 1996 ; Mulvey et al., 1998) and, from their 0002-4448  2001 SGM 145