Biology Reference
In-Depth Information
Chapter 11
Hybrid and potentially
pathogenic
Escherichia coli
strains
Victor A. Garcia-Angulo
1
, Mauricio J. Farfan
2
, and Alfredo G. Torres
1
1
University of Texas Medical Branch, Galveston, TX, USA,
2
Universidad de Chile, Santiago, Chile
DIFFUSELY ADHERENT
E. COLI
(DAEC)
Background
Definition
Diffusely adherent
E. coli
(DAEC) is one of six classical pathotypes of diarrhea-
genic
E. coli
(DEC), with the ability to adhere over the entire surface of HEp-2/
HeLa cells in a diffuse adherent (DA) pattern (
Scaletsky et al., 1984
). Analysis
of the virulence determinants of DAEC strains indicated that they are a diverse
group of strains with virulence genes homologous to those found in DEC strains
(EAEC, ETEC, or EPEC) or in extraintestinal
E. coli
strains associated with
urinary tract infections (UTIs) (
Czeczulin et al., 1999
;
Servin, 2005
).
History and evolution
To recognize DAEC strains from diarrheal stool samples of patients, the ability
of the bacteria to adhere to HEp-2/HeLa cells has been used (
Mathewson and
Cravioto, 1989
). This assay differentiated three adherence phenotypes: local-
ized, diffuse, or aggregative adherence (LA, DA, AA, respectively;
Figure 11.1
).
Analysis of the factors involved in the DA pattern led to the discovery of two
adhesins, the F1845 fimbriae and AIDA-I autotransporter (
Benz and Schmidt,
1989
;
Bilge et al., 1989
). Since then, DNA probes and PCR specific for these
virulence factors have been used for the identification of DAEC strains (
Jallat
et al., 1993
;
Vidal et al., 2005
), and to design epidemiological studies associat-
ing DAEC with diarrhea cases. In recent years, several groups have focused on
the study of F1845 fimbriae producing strains, since these fimbriae are related
to the Afa/Dr adhesins, which are expressed in a variety of pathogenic genetic
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