Chemistry Reference
In-Depth Information
17.1.1.1
Type 1 Fimbriae
Type 1 fi mbriae are cylindrical rods, approximately 7 nm wide and 1
m long [1] .
Their expression is phase variable, that is, the fi mbriae are not expressed on the
bacterial surface at all times. The carbohydrate specifi city of the lectin FimH is
for
μ
-mannose moieties (see Chapter 1, especially Figure 1.6, for sugar names,
structures and abbreviations).
E. coli
expressing type 1 fi mbriae are commensal habitants of the intestinal bacte-
rial fl ora [2, 3]. When entering the urinary tract they bind to glycoproteins carrying
high-mannose structures on epithelial cells (see Figure 4.2 and Chapters 6 and 8
for details on
N
-glycans) and cause urinary tract infections. FimH of bacterial iso-
lates from the urinary tract has been shown to have a higher affi nity for monoman-
nose as compared to FimH from fecal isolates, which recognizes mainly the trimer.
This is thought to be due to different allelic variants of FimH. Recently, it was
shown that the affi nity of
E. coli
type 1 FimH for monomannose can be increased
by shear stress that causes separation of two interacting domains, that is the
mannose-binding lectin domain and the fi mbriae - incorporating pilin domain, of
FimH (for further information on catch bond, please see Chapter 19.2). This may
favor attachment to epithelial cell ligands as opposed to free glycoproteins in the
urine, which otherwise would facilitate host cell protection.
Klebsiella pneumoniae
is an enterobacterium that can colonize the eyes, and the
gastrointestinal, respiratory and genitourinary tracts of healthy individuals. It may
produce an extended spectrum of
α
-lactamase enzymes, which cause resistance
against a multitude of different antibiotics. The bacterium has therefore emerged
as a serious health problem in hospitals, especially in neonatal intensive care units.
K. pneumoniae
can cause transfusion-mediated sepsis, pneumonia, urinary tract
infections, surgical site infections and conjunctivitis (eye infections). The mannose-
binding specifi city of
K. pneumoniae
FimH differs compared to
E. coli
FimH - a
difference presumably caused by the fi mbrial shaft. This is also the case for FimH
of
Salmonella typhimurium
, another member of the Enterobacteriaceae family that
exhibits tropism for gut epithelium. Swapping the FimH of an
E. coli
isolate onto
the fi mbrial shaft of
S. typhimurium
resulted in a switch of the
E. coli
FimH speci-
fi city to that of
S. typhimurium
FimH.
β
17.1.1.2
Type P Fimbriae
Type P fi mbriae [1] are common in
E. coli
isolates causing urinary tract infections.
They bind to globo series glycolipids which have internal or terminal Gal
1,4Gal
structures (see Chapters 10 and 30 for detailed information on glycolipid structure
and biosynthesis). Four serovariants,
pap
,
fso
,
fst
and
fel,
have been found, all quite
homologous to each other. The G subunit, of which three classes have been identi-
fi ed, is responsible for the lectin activity of the fi mbriae. Class I corresponds to
PapG and binds preferentially to globotriaosylceramide (Gb3) (the carbohydrate
sequences of structures referred to in the text are shown in the footnote of Table
17.1 for all bacterial lectins) on uroepithelial cells in the urinary tract. PapG
is quite rare in the
E. coli
population, and its clinical effects are consequently
poorly known. Class II, corresponding to FsoG and FstG, is common in
E. coli
strains causing upper urinary tract infections and pyelonephritis in man. It binds
α
