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FIGURE 13.3
Reproduced with permission from
Milgotina and Donnenberg,
(2009). Phenotypes
associated with bundle-forming pili expression in EPEC. (A) Transmission electron microscopy of
EPEC bundle-forming pili. (B) Phase-contrast micrograph of EPEC displaying localized adherence
to HeLa cells. Bacterial colonies indicated by arrows. (C) Phase-contrast image of auto-aggregation
of wild-type bacteria in liquid culture upon induction of BFP expression. Scale bars are indicated.
it must compete with the commensal microbiota. The finding that BfpB is pre-
dominantly distributed around the cell periphery (
Lieberman et al., 2012
) con-
trasts with previous findings that BfpL and BfpF localize to the poles of cells
expressing BFP (
Ramer et al., 2002
). The subcellular distribution of other T4P
in
E. coli
has not been studied.
ROLE IN VIRULENCE
Many T4P play a crucial role in colonization and virulence by binding to cell
surface receptors on the mucosal surface (
Strom and Lory, 1993
). BFP is a con-
firmed virulence factor (
Bieber et al., 1998
). BFP mediates the initial stages of
adherence to the host intestinal epithelium (
Cleary et al., 2004
;
Hyland et al.,
2006a,b
;
Zahavi et al., 2011
). Expression of BFPs is associated with a distinc-
tive adherence pattern on the surface of host cells called localized adherence
(LA) (
Scaletsky et al., 1984
), and the formation of aggregates in liquid culture
(
Anantha et al., 1998
) (
Figure 13.3
).
Bundlin sequences vary (
Blank et al., 2000
). Those belonging to the alpha
class bind to LacNac on the surface of host cells (
Hyland et al., 2006a,b,
2008
). A critical patch of surface-exposed residues determines this specificity
(
Humphries et al., 2009
).
The BFP and Type 3 Secretion systems together orchestrate environmen-
tal sensing, machine assembly, substrate transport, and regulatory feedback
networks that facilitate EPEC adherence to cells lining the intestinal epithelia.
While BFPs are responsible for the initial attachment to host cells (
Nougayrède
et al., 2003
), additional adhesins include the EspA filaments and intimin recep-
tor of a T3S system. This system acts as a molecular syringe through which
the bacteria inject numerous effector proteins into the host cell that modulate
host cell processes (
Kaper et al., 2004
;
Galán and Wolf-Watz, 2006
;
Dean and
Kenny, 2009
) (see Chapters 4, 14, and 15). The efficiency of intimate attachment
depends upon initial adherence mediated by BFP, as has been demonstrated
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