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Journal of Clinical Microbiology, July 1998, p. 2135-2137, Vol. 36, No. 7
Institute of Medical Microbiology,
Received 16 December 1997/Returned for modification 9 March
1998/Accepted 13 April 1998
Two sorbitol-fermenting (SF) Shiga toxin-producing
Escherichia coli (STEC) O157:H Shiga toxin
(verocytotoxin)-producing Escherichia coli (STEC)
strains of serotype O157:H (This work was presented in part at the 3rd International Symposium and
Workshop on Shiga Toxin (Verocytotoxin)-Producing Escherichia
coli Infections, Baltimore, Md., June 22 to 26, 1997 [abstr.
V9/I].)
The Czech SF STEC O157:H Both E. coli O157:H As shown in Table 1, the Czech SF STEC
O157:H RAPD PCR fingerprinting of genomic DNA (for a list and characteristics
of the strains tested, see Table 2)
showed that the Czech and German SF STEC O157:H
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Isolation and Characterization of Sorbitol-Fermenting Shiga Toxin
(Verocytotoxin)-Producing Escherichia coli O157:Hßtrains in the Czech Republic
ta
Bláhová,5 and
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ABSTRACT
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Abstract
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strains were isolated from
patients with hemolytic-uremic syndrome in the Czech Republic in 1995. Their phenotypic and genotypic characteristics and genomic DNA
fingerprints were identical or closely related to those of SF STEC
O157:H
strains isolated in Germany in 1988 to 1997. This indicates
that the Czech isolates belong to the SF STEC O157 clone which is
widespread in Germany. It is the first finding of the clone outside
Germany.
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Abstract
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(nonmotile) which ferment sorbitol and exhibit
-glucuronidase activity were first recognized in a 1988 outbreak of hemolytic-uremic syndrome (HUS) in Bavaria, Germany
(9). Since then, they have been identified as a significant cause of HUS and diarrhea in Germany (6). Based on their
phenotypic and genotypic features (1, 6, 12) and closely
related pulsed-field gel electrophoresis patterns (10, 12),
sorbitol-fermenting (SF) STEC O157:H
strains represent a new clone
within E. coli serogroup O157 which shares pathogenic
characteristics with non-sorbitol-fermenting (NSF) STEC O157:H7
(10, 12). Here we report the isolation of two SF STEC
O157:H
strains in the Czech Republic. The objective of the study was
to compare phenotypic and genotypic characteristics and to determine
genetic relatedness of the Czech and German SF STEC O157:H
strains to
find out whether the Czech isolates belong to the clone which is
widespread in Germany.
strains were isolated in August and October
1995 from two epidemiologically unrelated patients, aged 17 and 19 months, who were admitted to the University Hospital Motol, Prague,
Czech Republic, for HUS preceded by bloody diarrhea. Although no NSF
colonies were found in the patients' stool cultures on sorbitol
MacConkey agar (SMAC), both patients had evidence of E. coli
O157 infection. This was based on the presence of E. coli O157 antigen in their stools as detected by the E. coli O157 Antigen Detection enzyme-linked immunosorbent assay kit
(LMD Laboratories, Carlsbad, Calif.) (15) and on
significantly elevated titers of anti-O157 lipopolysaccharide
antibodies in their sera (1:10,240 and 1:20,480) as detected by the
indirect hemagglutination assay (3, 4). Slide agglutination
of SF colonies with anti-O157 antiserum (ITEST, Hradec
Králové, Czech Republic) and subsequent biochemical
identification of such colonies revealed SF E. coli O157 strains in stool cultures of both patients. Serotyping
by standard procedures (5) identified serotype O157:H
. The
vehicle of infection was not determined for either patient.
isolates were tested for fermentation
of D-sorbitol and
-D-glucuronidase activity
by tube tests (1), assayed for Shiga toxin 1 (Stx1), Stx2,
and Stx2c production by the Vero cell neutralization tests (8,
13), and examined for enterohemorrhagic E. coli
hemolysin (EHEC Hly) on enterohemolysin agar (2). Phage
patterns were determined (14) and compared with those of
German SF STEC O157 strains. The presence of
stx1, stx2,
stx2c, eaeA, and EHEC hly
genes was tested for by PCR procedures (10, 16, 17). Clonal
relatedness of the isolates with German SF STEC O157 strains was
determined by genomic DNA fingerprinting performed by randomly
amplified polymorphic DNA PCR (RAPD PCR) with primer 1247 (7). The RAPD PCR profiles were visualized under UV light
and photographed. A digital image of the gel was used to further
analyze the profiles by the GelCompar software package (Applied Maths,
Kortrijk, Belgium). Calculation of the similarity matrix was done by
the Pearson product-moment correlation coefficient method
(18). Hierarchic clustering was achieved by using the
unweighted-pair-group method with the arithmetic averages clustering
algorithm (18).
isolates had identical phenotypic and genotypic
characteristics which were at the same time identical with those of 24 German SF STEC O157:H
strains isolated in 1988 to 1996. The only
exception was the absence of the stx2 gene in
isolate 230/95, which lost Stx2 production within 1 month after
isolation, before it was genotyped. A new phage type designation (phage
type 88) was assigned to the Czech and German SF STEC O157:H
isolates
which shared a phage pattern that did not correspond to any of the
previously recognized E. coli O157 phage types
(14).
TABLE 1.
Phenotypic and genotypic characteristics of Czech SF STEC
O157:H
isolates compared with those of German SF STEC
O157:H
strains
isolates had
identical or closely related profiles that markedly differed from those
of NSF STEC O157:H7/H
(Fig. 1).
Analysis of the RAPD PCR profiles by the Pearson product-moment
correlation method and by the unweighted-pair-group method with
arithmetic averages clustering clearly distinguished three clusters of
strains (Fig. 2). Nine SF STEC O157:H
strains from Germany and the Czech SF STEC O157:H
isolates gave a
cluster with a nearly congruent pattern, thus showing high relatedness. The second cluster contained all NSF STEC O157:H7/H
strains; they
were also closely related to each other but could be clearly distinguished from the SF STEC O157:H
strains. The third group consisted of two Stx-negative strains of serotypes O157:H19 and O157:H45; these strains were not related to either NSF or SF STEC O157:H7/H
(Fig. 2). Taken together with the other phenotypic and
genotypic results, it can be concluded that the Czech SF STEC O157:H
strains belong to the clone which is resident in Germany.
TABLE 2.
List and characteristics of SF and NSF E. coli
O157 strains analyzed by RAPD PCR fingerprinting

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FIG. 1.
Agarose gel showing RAPD PCR fingerprints of
representative SF and NSF STEC O157 strains obtained with primer 1247. NSF E. coli O157:H7/H
strains 3075/96 (lane 1), 3010/96
(lane 2), EDL933 (lane 3), 6651/96 (lane 4), and 3817/96 (lane 5) are
depicted. The SF E. coli O157:H
strains were Czech
isolates 221/95 (lane 6) and 230/95 (lane 7) and German isolates
1529/97 (lane 8), 7713/95 (lane 9), and 1995/96 (lane 10). The
molecular weight marker (M2) was DNA marker VI (Boehringer Gmbh); the
molecular sizes of the fragments are (in base pairs) 2,176, 1,766, 1,230, 1,033, 653, 517, 453, 394, 298, 234, and 220. The internal
standard (M1) consisted of a 1,600-bp and a 244-bp PCR product. In
addition, internal standards were included in each lane.

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FIG. 2.
Dendrogram derived from RAPD PCR data for Czech and
German SF STEC O157:H
strains, NSF STEC O157:H7/H
strains, and SF
Stx-negative E. coli O157:H19/H45 strains with the GelCompar
software package. The characteristics of the strains are given in Table
2. The similarity scale is shown above the dendrogram (a similarity
index of
80% indicates clonal relatedness).
This is the first report that SF STEC O157:H
strains belonging to the
German clone can be a cause of HUS outside Germany. Although the
vehicle of infection was not identified, the fact that none of the
Czech patients had histories of travelling in Germany or consumption of
foods imported from Germany makes domestic origin of infection very
likely. Our findings thus suggest that the SF STEC O157 clone has begun
to spread from Germany and that these strains can emerge as a public
health problem in other countries. This has important diagnostic
implications, emphasizing the need for diagnostic procedures which
allow detection of infection with both NSF and SF E. coli
O157 strains. In our study, combination of stool culture on SMAC with
E. coli O157 stool enzyme-linked immunosorbent assay and
anti-O157 serology enabled us to detect E. coli O157
infection despite the absence of NSF colonies on SMAC, thus aiming our
diagnostic efforts towards searching for SF E. coli O157
strains. The procedures which have been successfully used to detect SF
STEC O157 strains in German studies have included genetic methods
(6, 9, 11) and the technique of immunomagnetic separation
followed by plating magnetic particles with attached O157 bacteria on
SMAC (11). Here, it should be remembered that SF STEC O157
strains, in contrast to NSF STEC O157:H7, do not grow on a selective
cefixime-tellurite SMAC (11), since they do not tolerate
high tellurite concentrations (12). Although the SF STEC
O157:H
strains possess EHEC hly genes, no enterohemolytic phenotype could be observed (Table 1). This finding has consequences for the detection of such STEC in stool samples. While enterohemolysin agar plates have been successfully used for detecting EHEC
Hly-producing NSF STEC O157:H7 (2), this method fails to
detect nonhemolytic SF STEC O157:H
as characterized in this study.
Consistent use of appropriate diagnostic methods for clinical and
epidemiological studies is necessary to further evaluate significance
of SF STEC O157 strains in human disease, to identify their reservoirs,
and, based on that, to implement effective prevention of human
disease.
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ACKNOWLEDGMENTS |
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This study was supported by grant IGA 2063-3 from the Ministry of Health of the Czech Republic and by grant BMH4-CT96-0970 from the European Communities.
We thank T. Cheasty, Central Public Health Laboratory, London, United
Kingdom, for confirming the serotype, Stx genotype, and phage type of
Czech E. coli O157:H
isolates. The excellent technical
assistance of B. Plaschke and A. Reischelová is greatly appreciated.
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FOOTNOTES |
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* Corresponding author. Mailing address: Institute of Medical Microbiology, The 2nd Medical Faculty, Charles University, V úvalu 84, 150 06 Prague 5-Motol, Czech Republic. Phone: 420-2-2443-5351. Fax: 420-2-2443-2020. E-mail: jan.janda{at}lfmotol.cuni.c2.
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