Uropathogenic Escherichia coli - Escherichia coli: Pathotypes and Principles of Pathogenesis - page 277

( Allsopp et al., 2010 ). However, in two other UPEC strains that express UpaH
there was no significant defect in colonization when upaH was deleted. Thus,
UpaH appears to be a strain-specific virulence factor ( Allsopp et al., 2010 ).
UpaB
Although there is no significant difference in the prevalence of UpaB in UPEC
(58%) versus fecal isolates (42%), UpaB is disrupted or absent in the genomes
of all diarrheagenic E. coli genomes ( Allsopp et al., 2012 ). UpaB is expressed
by the prototypical pyelonephritis isolate E. coli CFT073 and is present on the
surface of the bacterium. Demonstrating the potential for UpaB to contribute
to uropathogenesis, UpaB from E. coli CFT073 expressed in E. coli K-12 was
found to mediate adherence to the extracellular matrix proteins fibronectin,
fibrinogen, and laminin, but not collagen types I-V, elastin, or heparin sul-
fate ( Allsopp et al., 2012 ). Furthermore, when tested in vivo, wild-type E. coli
CFT073 outcompeted Δ upaB in colonization of the murine bladder ( Allsopp
et al., 2012 ), demonstrating that this autotransporter protein is involved in uro-
pathogenesis.
UpaC
UpaC, which was characterized alongside UpaB, is found at similar prevalence
in UPEC strains (47%) as in commensal E. coli strains (34%) ( Allsopp et al.,
2012 ), however, UpaC is disrupted in the commensal isolates E. coli MG1655,
DH1, and HS. While UpaC was undetectable by western blot from wild-type
E. coli CFT073, deletion of hns enhanced UpaC expression, demonstrating that
H-NS acts a repressor of UpaC expression. When over-expressed in E. coli
K-12, UpaC promotes biofilm formation to abiotic surfaces. However, when
assessed in co-challenge in the murine ascending UTI model, there was no sig-
nificant difference in in vivo fitness between wild-type E. coli CFT073 and
Δ upaB ( Allsopp et al., 2012 ). Therefore, UpaC may play only a subtle role
in vivo.
Ag43a
Antigen 43a (encoded by fluA , Ag43a, UpaF) is a surface-located adhesin that
undergoes phase variation and is associated with urovirulence ( Anderson et al.,
2003 ). Ag43a mediates cell aggregation and biofilm formation on abiotic surfaces
when expressed from a plasmid in E. coli K-12. However, in E. coli CFT073,
cell aggregation and biofilm formation were not affected by Ag43a, as this is a
short surface-associated structure and the longer surface structures such as fla-
gella and fimbriae expressed simultaneously by E. coli CFT073 do not allow
the close cell-cell contact necessary for these phenotypes to be observed ( Ulett
et al., 2007a ). In the mouse model of ascending UTI, deletion of fluA , the gene
encoding Ag43a in E. coli CFT073, reduced long-term persistence in the bladder
( Ulett et al., 2007b ). Therefore, Ag43a may have a role in persistence in vivo.