Uropathogenic Escherichia coli - Escherichia coli: Pathotypes and Principles of Pathogenesis - page 274

CFT073 and the auf mutant and the mutant was not outcompeted by wild-type
in competition studies ( Buckles et al., 2004 ).
Pix fimbriae
Pix fimbriae are a relatively rare fimbrial type found in 8% of UPEC compared
to 4% of fecal E. coli strains ( Spurbeck et al., 2011 ). Pix fimbriae were initially
discovered on a pathogenicity island found in the uropathogenic E. coli strain
X2194 ( Lugering et al., 2003 ). Pix fimbriae are related to P fimbriae, but are dif-
ferentially regulated due to a truncation in the regulatory region associated with
P fimbriae. Expression of Pix was found to be temperature-dependent during
stationary phase. Pix fimbriae promote adherence to HeLa cells ( Lugering et al.,
2003 ), demonstrating that these fimbriae, although rare, can be an important
virulence factor for some UPEC. The importance of Pix fimbriae has yet to be
tested in the mouse model of ascending UTI.
Dr/Afa fimbriae
Dr and Afa adhesins are a family of E. coli adhesins that recognize the Dr blood
group antigen (a cell membrane protein in erythrocytes also called the decay-
accelerating factor) as their receptor ( Nowicki et al., 1990 ). While some Dr family
adhesins are afimbrial adhesins, such as AFA-I and AFA-III, others are fimbrial
adhesins like F1845 and Dr fimbriae ( Nowicki et al., 1990 ). The best-studied
member of the Dr family of adhesins, the Dr fimbriae (aka O75X), are found in
7% of UPEC compared to 2% of fecal E. coli strains ( Spurbeck et al., 2011 ) and
bind type IV collagen in vitro ( Westerlund et al., 1989 ). In vivo, Dr fimbriae bind
to peritubular connective tissue in the human kidney ( Nowicki et al., 1986 ), the
connective tissue between muscle cell layers in the bladder, human neutrophils
( Johnson et al., 1995 ), and weakly to epithelial cells ( Virkola et al., 1988 ). Dr
fimbriae also facilitate cell invasion ( Goluszko et al., 1997 ; Fang et al., 2004 ; Das
et al., 2005 ), allowing bacteria to avoid the humoral immune response by hiding
within the intracellular space. Vaccination with purified Dr fimbriae reduced mor-
tality associated with UTI in a mouse model of infection ( Goluszko et al., 2005 ),
however, since the majority of UPEC do not encode these fimbriae, vaccination
against Dr fimbriae would prevent only a minor subset of UPEC infections.
Putative fimbriae (Yeh, type IV pili 1 and 2, Yfc)
The presence of two putative fimbriae encoded by E. coli CFT073, Yfc fim-
briae (encoded by yfcOPQRSUV , present in 73% UPEC isolates v. 33% fecal
isolates) and type IV pilus 2 (encoded by c2394-c2395 , present in 51% UPEC
v. 12% fecal isolates), are correlated with uropathogenic isolates ( Spurbeck
et al., 2011 ). However, Yeh fimbriae (encoded by yehABCD , present in 94% of
E. coli isolates) and type IV pilus 1 (encoded by ppdD , hofB , and hofC , present
in 99% of E. coli isolates) are found ubiquitously in the E. coli population, and
are therefore, not markers of pathogenic isolates.