Role of type 1 somatic pili (fimbriae) in mucosal attachment of the enteroadherent Escherichia coli, strain RDEC-1, in rabbits.

We have previously shown that attachment of the rabbit enteroadherent Escherichia coli, strain RDEC-1, to ileal brush borders in vitro is mediated by both mannose-resistant, AF/R1 pili and mannose-sensitive, type 1 pili. Because the role of type 1, somatic pili as adhesins that mediate bacterial enteroadherence in vivo remains controversial, we examined adherence of RDEC-1 expressing either type 1 pili or AF/R1 pili to rabbit ileum in ligated loops and after oral infection of rabbits. A rabbit fecal commensal E. coli, 640, which also expressed type 1 pili was used as a control. After oral infection of rabbits we evaluated: (a) diarrhea, (b) fecal shedding of organisms, (c) luminal colonization of jejunum and ileum, and (d) mucosal adherence of bacteria to jejunum, ileum, and colon. RDEC-1 expressing either type 1 or AF/R1 pili adhered to enterocytes both in ileal ligated loops and in the distal ileum, cecum, and proximal colon of infected rabbits. In contrast, enteroadherence of 640 was not observed. Diarrhea developed in rabbits challenged with either type 1 or AF/R1 piliated RDEC-1, but not in rabbits fed 640. Seven days after infection of rabbits with RDEC-1 bearing type 1 pili, luminal colonization of jejunum (4.22 +/- 0.55 CFU/g, X +/- SE) and ileum (6.34 +/- 0.55) was the same as after infection with AF/R1 piliated RDEC-1 (jejunum 4.47 +/- 0.20, ileum 5.81 +/- 0.70) and significantly greater than luminal colonization by type 1 piliated 640 (jejunum less than 2.22 +/- 0.14, ileum less than 2.06 +/- 0.15).(ABSTRACT TRUNCATED AT 250 WORDS)