Biology Reference
In-Depth Information
Diagnosis
At first, the HEp-2/HeLa cells adherence assay was widely used to identify
DAEC strains. However, the identification and characterization of F1845 and
AIDA-1 led to the use of these adhesins as markers for DAEC strains. It is
important to note that a significant number of strains with a DA phenotype are
negative for both markers and therefore are not classified as DAEC (
Jallat et al.,
1993, 1994
). Therefore, additional studies to identify novel, more reliable mark-
ers for the DAEC pathotype are warranted. Considering that the prevalence of
Afa/Dr adhesins in DAEC is higher than that of AIDA-I, numerous assays to
diagnose Afa/Dr DAEC have been developed using the F1845 or related adhes-
ins. Among these assays, the molecular detection of genes located in the Afa/Dr
operon has been explored. Different DNA probes for colony hybridization have
been assayed, but this is a time-consuming technique that requires trained per-
sonnel, making difficult its implementation in a clinical laboratory. PCR-based
techniques, such as multiplex PCR, to identify
E. coli
colonies obtained from
cultures or stool samples offer a more practical, rapid and accurate diagnosis.
Multiplex PCR assay to identify all six
E. coli
pathotypes has provided a valu-
able tool for epidemiological studies (
Vidal et al., 2005
).
Treatment
Diarrheal illness caused by DAEC, as well as other DEC pathotypes, might
be ameliorated by specific antimicrobials, however clinical data demonstrat-
ing their efficacy are lacking. Moreover, DAEC strains are associated with a
high frequency of antibiotic resistance. DAEC strains have presented high lev-
els of resistance to antibiotics commonly used to treat enteric infections, com-
pared to the rest of DEC strains (
Ochoa et al., 2009
). Moreover, the majority
of the DAEC strains with resistance to multiple antibiotics are associated with
conjugative plasmids, a situation that not only hinders the antibiotic treatment,
but also facilitates the dissemination of the antibiotic resistance genes between
enteric pathogens (
Lopes et al., 2005
). In many countries, the implementation of
oral rehydration is the treatment of choice for DEC infections, including DAEC.
This strategy has significantly reduced deaths caused by diarrhea, but in severe
cases, an antibiotic treatment might be necessary. In this case, the knowledge
of the profile of antibiotic susceptibility can guide the selection of an adequate
antimicrobial management. UTIs caused by DAEC are treated according to
guidelines for other
E. coli
UTIs (see Chapter 9).
Immune response
In order to investigate the role of DAEC in the development of diarrhea, volun-
teers were fed reference DAEC strains. None of them developed diarrhea and
only of small number developed IgG or IgA antibodies to DAEC (
Tacket et al.,
1990
). These results and the controversial role of DAEC as a diarrhea-causing
pathogen have reduced the interest to analyze the immune response against this
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