Biology Reference
In-Depth Information
Iron uptake systems
A wide variety of strategies for acquiring iron have been developed by EAEC
and other pathogenic E. coli , the most common being the production of sidero-
phores and the utilization of heme ( Okeke et al., 2004 ). Interestingly, E. coli
O104:H4 possesses the genes encoding for the siderophore aerobactin, an iron
uptake system that is linked to pathogenesis in extraintestinal E. coli s trains and
commonly present in EAEC clinical isolates ( Torres et al., 2001 ). A recent study
in which a murine model mimicking enteropathogenicity of E. coli strains, in
combination with bioluminescent imaging technology, was used to visualize
the site of intestinal colonization as well as to define the role of the aerobactin
transport system in the virulence of E. coli O104:H4 ( Torres et al., 2012 ). The
study found that the murine intestinal cecum was colonized by E. coli O104:H4,
with bacteria persisting up to 7 days after intragastric inoculation. Further, the
isogenic aerobactin receptor ( iutA ) mutant was out-competed by the wild-type
E. coli O104:H4 during in vivo colonization, being unable to persist in the
cecum and suggesting that this iron transport system is essential for intestinal
fitness ( Torres et al., 2012 ).
Antibiotic resistance
E. coli O104:H4 contains an array of antibiotic resistance genes conferring
resistance to ampicillin, amoxicillin/clavulanic acid, piperacillin/sulbactam,
piperacillin/tazobactam, cefuroxime, cefuroxime-axetil, cefoxitin, cefotaxime,
cetfazidime, streptomycin, nalidixic acid, tetracycline, trimethoprim and sul-
famethoxazol ( Scheutz et al., 2011 ), exceeding the numerous resistance genes
found in previous outbreak strains. The convergence of multiple antibiotic resis-
tance genes not commonly found in EAEC strains suggests that this lethal bac-
terium might acquire the antibiotic markers by horizontal gene transfer of the
multiresistant plasmid ( Bezuidt et al., 2011 ). Despite the multiantibiotic resis-
tance properties of E. coli O104:H4 and that antibiotic treatment of STEC infec-
tions is discouraged because it might increase HUS development, a number of
patients in the German outbreak received prophylactic azithromycin treatment
in combination with the C5 antibody eculizumab (see below) ( Nitschke et al.,
2012 ). Investigation of the patients receiving this treatment demonstrated that
azithromycin administration was associated with a lower frequency of STEC
O104:H4 shedding in several cases ( Nitschke et al., 2012 ).
Clinical manifestations
Transmission
Shiga-toxin-producing E. coli serotype O104:H4 has been rarely associated with
human cases in the past and has never been reported in animals ( Auvray et al.,
2012 ). Epidemiologic, microbiologic, and food trace-back and trace-forward
investigations indicated that fenugreek sprouts were the vehicle of infection
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