The Ability Of Crohn'S Associated E. Coli To Invade Caco-2 Cells Is Related To The Presence Of A Gene Encoding Long Polar Fimbriae

E. coli strains that invade and replicate within cultured epithelial cells and macrophages are increasingly associated with Crohn's disease (CD). Knowledge of the bacterial factors conferring this pathogenic behavior is incomplete. We examined the ability of 47 ileal E. coli strains to invade caco-2 cells and replicate in J774 macrophages by their disease association (Crohn's ileitis, CD, 24 strains; normal ileum, NI, 23 strains), phylogroup (A, B1, B2, D), and virulence gene content (determined by microarray, subtractive hybridization and PCR). There was no effect (P>0.05) of disease association on the degree of invasion (median, log10 cfu/ml: CD 2.86, NI 2.6) or replication (median, %: CD 221, NI 315). The prevalence of E. coli strains with an adherent and invasive (AIEC) pathotype was similar in CD (13 of 23 strains) and NI (9 of 22 strains) (P>0.05). There was no effect of E.coli phylogroup on invasion or persistence (P>0.05). A screen for genes encoding virulence in E. coli (microarray of 22 E.coli strains: 11 CD, 11 NI), and genes present in AIEC but absent in commensal DH5 (subtractive hybridization of one AIEC strain from each phylogroup), identified ratA. Pmt,I colV, hcp, lpfA-141, lpfA-154 kpsMI,I fyuA, iss, malX, typeII, typeIV, afaBC, focG, ibeA, papC, sfaDE, cnf1, Stx1 and eae as putative virulence determinants. The presence or absence of these genes in 47 ileal E. coli strains was determined by PCR and related to invasion and persistence. The presence of lpfA-154, a gene encoding long polar fimbriae, was associated with increased invasion of caco-2 cells (P=0.02: median, log10 cfu/ml, lpfA+ 3.50, lpfA2.05). LpfA-154 was present in 15 of 22 (68%) AIEC strains. It's presence in ileal E. coli was influenced by phylogroup (present in 93% B1, 50% D and 15% A, but absent from B2 strains), but not by disease association (50% of CD vs. 33% of NI strains). DNA sequence analysis of lpfA-154, cloned from a B1 CD isolate, showed highest homology to E. coli E24377A (an ETEC strain) and Shigella boydii CDC3083-94. We conclude that a gene encoding long polar fimbriae (lpfA-154) is associated with increased invasion of caco-2 cells by ileal E. coli, and is common in E. coli with an AIEC pathotype. LpfA is involved in the adhesion of Salmonella to Peyer's patches, and may influence host-E. coli interactions in a CD susceptible individual.