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Journal of Clinical Microbiology, June 1998, p. 1777-1780, Vol. 36, No. 6
Laboratoire de Bactériologie,
Received 2 December 1997/Returned for modification 17 February
1998/Accepted 17 March 1998
From August 1996 to May 1997, six verotoxin-producing
Escherichia coli (VTEC) strains were isolated from stool
specimens of adults suffering from hemolytic-uremic syndrome (HUS). All
the isolates were stx2 positive and belonged to
different serotypes: O6:H4, O91:H10, O91:H21, O rough:H16, OX3:H Hemolytic-uremic syndrome (HUS) is
characterized by acute hemolytic anemia, thrombocytopenia, and acute
renal failure. In some cases, these three clinical features are
associated with neurological manifestations and fever. The association
between HUS and verotoxin-producing Escherichia coli (VTEC)
infection is now well established, and usually prodromic
gastroenteritis, frequently including bloody diarrhea, is observed
(9). Cases of HUS caused by VTEC have been identified in all
age groups but most frequently in infants and young children, and they
are observed either during the course of outbreaks of VTEC infections
or as sporadic cases. Contamination occurs via consumption of
contaminated food, and most of the clinical signs observed are due to
the absorption from the gastrointestinal tract of Shiga-like toxins
(Stx) produced by the bacteria. Two types of Shiga-like toxins (also
called verotoxins), Stx1 and Stx2, which presumably cause
microangiopathic hemolytic anemia as a result of endothelial-cell
injury, have been isolated. Other bacterial virulence factors may play
a role in the pathological process, including an outer membrane
protein, intimin, the product of the chromosomal gene eae,
which is involved in bacterial adhesion to intestinal cells
(6), as well as a plasmid-encoded enterohemolysin (Ehly)
which has a cytolytic effect (20).
E. coli O157:H7 is the worldwide serotype of VTEC most
commonly isolated from HUS patients. Other serogroups have been
implicated (O26, O55, O103, O111, and O128) (3, 14, 17, 23),
but their occurrence is likely to be underestimated, because isolation of non-O157:H7 VTEC still remains a challenge. Unlike most of the
O157:H7 isolates, the majority of non-O157:H7 VTEC strains ferment
sorbitol and therefore cannot be isolated by using media such as
sorbitol MacConkey agar. Molecular biological and immunological techniques based on the detection of verotoxin genes and toxins, respectively, are so far the most reliable methods for detecting these
pathogens in clinical specimens.
Patients and clinical features.
The average number of adults
with HUS admitted to the medical intensive-care unit of the
Clermont-Ferrand hospital used to be one every 18 months. (This
hospital serves a large geographical area with approximately 1.3 million residents.) Between August 1996 and May 1997, this number
increased considerably; 14 patients with clinical and biological
evidence of HUS were admitted. In six cases, a VTEC strain was
identified in the patients' stools by stx-specific PCR. The
patients' mean age was 64 ± 19 years (range, 39 to 84 years).
The male-to-female ratio was 1:5. All the patients developed HUS,
defined as a Coombs-negative microangiopathic hemolytic anemia,
thrombocytopenia without signs of disseminated intravascular
coagulation, and acute renal failure (see Table 1). One of them (patient 1) had
previously been admitted to the gastroenterology unit with severe
abdominal pain and bloody diarrhea. Eleven days later, development of
macroscopic hematuria and acute renal failure prompted her transfer to
the intensive-care unit. Coombs-negative microangiopathic hemolytic
anemia was defined as a hemoglobin level of <10 g/dl, intravascular
hemolysis (serum haptoglobin, Isolation of VTEC strains by stx-specific PCR.
Fecal samples were both cultured in Luria-Bertani (LB) broth (Difco
Laboratories, Detroit, Mich.) and streaked out on Drigalski plates
(Biomerieux, La Balme les Grottes, France), and they were then
incubated at 37°C for 18 h. Bacteria from 1 ml of the LB broth
culture or from at least 10 single colonies grown on Drigalski agar and
previously suspended in 1 ml of saline were harvested, resuspended in
200 µl of sterile water, and incubated at 100°C for 10 min.
Following centrifugation of the lysate, 10 µl of the supernatant was
used in PCR. Oligonucleotides specific for amplification were
5'-ACCCTGTAACGAAGTTTGCG-3' and
5'-ATCTCATGCGACTACTTGAC-3' for stx1
and 5'-ATCCTATTCCCGGGAGTTTACG-3' and
5'-GCGTCATCGTATACACAGGAGC-3' for stx2
(4, 18). The PCR cycle included denaturation for 1 min at
94°C, primer annealing for 1 min at 55°C, and extension for 1 min
at 72°C (30 cycles) in a Perkin-Elmer Cetus DNA thermal cycler. Each
of the primers was used at 0.125 mM, with 0.2 mM each deoxynucleoside
triphosphate (Boehringer Mannheim, Meylan, France), 50 mM KCl, 10 mM
Tris-HCl (pH 8.3), 1 mM MgCl2, and 1 U of Taq
DNA polymerase (Appligène-Oncor, Illkirch, France). The reaction
products were then analyzed by electrophoresis on 2% agarose gels
after staining with ethidium bromide. DNA from the reference strain
E. coli EDL 933 and a reagent blank, which contained all
components except the template DNA, were included as positive and
negative controls, respectively. The identities of the PCR products
were then confirmed by Southern hybridization after transfer to Hybond
N+ nylon membranes (Amersham International, Amersham, United Kingdom)
and hybridization with a 1.1-kb BamHI stx1-specific or a 0.8-kb PstI
stx2-specific DNA probe obtained from the
recombinant plasmids pJPN37-19 and pNN111-19, respectively (16). DNA probes were labeled by random priming using the
enhanced chemiluminescence system (ECL; Amersham International)
according to the manufacturer's specifications, and hybridized filters
were exposed to ECL-Amersham film. As shown in Fig.
1, PCR products of 584 bp were detected
with the stx2-specific primers with all stool
specimens, but none of them gave a positive reaction with the
stx1-specific primers. Similar results were
obtained by colony hybridation using Stx1- and Stx2-specific DNA probes
(data not shown).
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Non-O157:H7 Stx2-Producing Escherichia
coli Strains Associated with Sporadic Cases of
Hemolytic-Uremic Syndrome in Adults
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ABSTRACT
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Abstract
Text
References
, and
O nontypeable:H
. The enterohemolysin (Ehly)-encoding genes were
detected in two isolates, and none of the isolates harbors the intimin
(Eae)-encoding gene. These findings suggest that
stx2-positive non-O157:H7 VTEC is a major cause
of HUS in adults and that several sources of pathogens are responsible
for local endemic infections.
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TEXT
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Abstract
Text
References
0.1 g/liter), negative results of
Coombs' test, and fragmented red cells and schistocytes on blood
smear. Acute renal failure occurred in all the patients enrolled; four
of them required renal replacement therapy. Fever (body temperature of >38°C) was present in four patients. Prodromal bloody diarrhea was
observed in two patients, and nonbloody diarrhea was observed in four.
All patients were treated with plasma exchanges, and none of them died.
The mean number of plasma exchange treatments was 11 ± 2.
TABLE 1.
General, biological, and clinical data of patients during
the acute phase and characteristics of the E. coli strains
isolated from patients' stool specimens

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FIG. 1.
Agarose gel electrophoresis of DNA fragments obtained by
multiplex PCR with primers specific for stx1
(140 bp) and stx2 (584 bp) (A) and with primers
specific for ehly (340 bp) (B) performed with genomic
extracts from different E. coli strains: EDL 933, stx1-, stx2-, and
ehly-positive O157:H7 reference strain; CH011, CH013, CH014,
CH015, CH016, and CH017, isolates from patients 1 through 6, respectively. M.W., 1-kb ladder of molecular size markers (Boehringer
Mannheim).
Bacterial identification and characterization.
stx-positive isolates were identified biochemically by using
an API 20E test (Biomerieux). All the isolates fermented sorbitol. Determination of their serotypes performed by the International E. coli and Klebsiella Reference Center in
Copenhagen, Denmark, revealed that they belonged to different
serotypes: O6:H4 (patient 1), O91:H10 (patient 2), O91:H21 (patient 3),
O rough:H16 (patient 4), and OX3:H
(patient 5). The O-antigenic
nature of the VTEC isolate from patient 6 could not be determined
(O+:H
). Ehly-specific genes were detected by PCR using the primers
5'-CACACGGAGCTTATAATATTCTGTCA-3' and
5'-AATGTTATCCCATTGACATCATTTGACT-3'. Conditions similar to those used for detection of stx genes were used, and the PCR
products were identified by hybridization with a 3.4-kb
HindIII fragment from pEO40 (20). Two
strains, those isolated from patients 3 and 4, harbored Ehly-specific
sequences as determined by PCR (Fig. 1) and hybridization; the same two
isolates produced detectable hemolysis after 18 h of growth at
37°C on 5% washed sheep blood agar plates. The presence of
eae was detected by dot blot hybridization; bacteria were
grown in LB broth at 37°C overnight, and DNA was extracted by
successive action of lysozyme, proteinase K, and Sarkosyl, followed by
a purification step in a cesium chloride gradient. Hybridization was
performed as described above by using a DNA probe specific for
eae, i.e., a 1.4-kb fragment from an O157:H7 clinical
isolate covering the entire eae open reading frame. DNAs
from the reference strains E. coli EDL 933 and DH5
were
included as positive and negative controls, respectively. None of the
VTEC isolates hybridized with this DNA probe when they were tested
under high-stringency conditions.
Virulence factors other than toxins are likely to be required during the pathological process, including adherence factors and/or cytolysins. Among the six VTEC strains isolated in this study, none harbored the intimin-encoding gene (eae), which is involved in the attachment and effacing process, and Ehly sequences were detected in only two isolates. The presence of eae has mostly been described in O157:H7 isolates, but eae-negative non-O157 VTEC strains are also capable of causing disease indistinguishable from that caused by eae-positive O157:H7 (7, 11). It is likely that eae-negative VTEC strains pathogenic for humans may possess adherence factors other than Eae; investigations are currently being performed with isolates from this study in order to identify their adherence factors.
The role of the plasmid-encoded Ehly in the pathologic process of VTEC strains is not yet known. Ehly's produced by VTEC strains belong to the RTX (defined as repeats in toxin) toxin family and are closely related to the E. coli
hemolysin. They might act by
lysing eucaryotic cells or by modulating the immune response, thus
enhancing the virulence of VTEC. Previous studies demonstrated that
patients infected with Ehly-positive VTEC were at a higher risk for
developing HUS than patients infected with Ehly-negative strains
(21). Only two bacterial isolates from this study harbored Ehly-encoding genes, indicating that synthesis of Ehly is not an
absolute prerequisite for HUS development, although it might contribute.
From this study, we conclude that Shiga toxin-producing bacteria of
serotypes other than O157:H7 can cause serious disease, as has been
observed in several other instances. Cases of HUS due to non-O157:H7
E. coli are usually sporadic, unlike most of the infections
due to serotype O157:H7. The reasons for this difference have not yet
been addressed; it might be due to variations in the strains'
virulence, but difficulties in identification of non-O157:H7 E. coli strains might also contribute to underestimation of their
virulence potential. Although the cases of HUS observed in this study
occurred in the same geographical area in a relatively short period (10 months), characterization of the VTEC isolates demonstrated that they
were not related to each other. This might reflect an endemic
situation, and since HUS represents the tip of an iceberg of clinical
complications, it is likely that the number of mild infections is
greatly underestimated. Development of diagnostic tools allowing
detection of VTEC regardless of serotype is therefore urgently needed.
Rapid and efficient detection of VTEC should be performed not only with
patients suffering from HUS, but with anyone suffering from bloody
diarrhea, in order to prevent both severe development of the disease
and further spread of the pathogens.
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ACKNOWLEDGMENTS |
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We thank Kristin Swihart for critical review of this paper.
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FOOTNOTES |
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* Corresponding author. Mailing address: Laboratoire de Bactériologie, Faculté de Pharmacie, Université d'Auvergne, 28, place H. Dunant, 63001 Clermont-Ferrand, France. Phone: (33) 4 73 60 80 19. Fax: (33) 4 73 27 74 94. E-mail: Christiane.forestier{at}u-clermont1.fr.
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