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Appl Environ Microbiol, July 1998, p. 2449-2453, Vol. 64, No. 7
Hygiene Institute Hamburg, Division of
Bacteriology, National Reference Centre for Enteric Pathogens,
D-20539 Hamburg, Germany
Received 9 February 1998/Accepted 7 April 1998
The presence of a hemolysin-encoding gene, elyA or
hlyA, from Shiga toxin-producing Escherichia
coli (STEC) was detected by PCR in each of 95 strains tested. PCR
products of elyA from human STEC isolates of serovars
frequently detected in Germany, such as O157:H
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Detection of Hemolysin Variants of Shiga
Toxin-Producing Escherichia coli by PCR and Culture on
VancomycinCefixime-Cefsulodin Blood Agar
, O103:H2, O103:H
,
O26:H11, and O26:H
, showed nucleotide sequences identical to
previously reported ones for O157:H7 and O111:H
strains. Compared to
them, four elyA amplicons derived from human isolates of
rare STEC serovars showed identity of about 98% but lacked an
AluI restriction site. However, the nucleotide sequence of
an amplicon derived from a porcine O138:K81:H
STEC strain was
identical to the corresponding region of hlyA, encoding alpha-hemolysin, from E. coli. This hlyA
amplicon showed 68% identity with the nucleotide sequence of the
corresponding elyA fragment. It differed from the
elyA PCR product in restriction fragments generated by
AluI, EcoRI, and MluI. Of the 95 representative STEC strains, 88 produced hemolysin on blood agar
supplemented with vancomycin (30 mg/liter), cefixime (20 µg/liter),
and cefsulodin (3 mg/liter) (BVCC). The lowest added numbers of two to
six STEC CFU per g of stool or per ml of raw milk were detectable on
BVCC plates after seeding of the preenrichment broth, modified tryptic soy broth (mTSB) supplemented with novobiocin (10 mg/liter), with 16 STEC strains. These strains represented the seven prevailing serovars
diagnosed from German patients. However, with ground-beef samples, PCR
was essential to identify the lowest added numbers of two to six STEC
CFU among colonies of hemolyzing Enterobacteriaceae, such
as Serratia spp. and alpha-hemolysin-producing E. coli. We conclude that preenrichment of stool and food samples in
mTSB for 6 h followed by overnight culturing on BVCC is a simple
method for the isolation and presumptive identification of STEC.
*
Corresponding author. Mailing address: Hygiene
Institute Hamburg, Division of Bacteriology, Marckmannstr. 129a,
D-20539 Hamburg, Germany. Phone: 49-40-78964270. Fax: 49-40-78964274. E-mail: hygiene.institut{at}hamburg.de.
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