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Journal of Clinical Microbiology, May 1997, 1066-1070, Vol 35, No. 5
PI Fields, K Blom, HJ Hughes, LO Helsel, P Feng and B Swaminathan
Recent outbreaks of disease caused by Escherichia coli O157:H7 have focused
much attention on this newly emerged pathogen. Identification of the H7
flagellar antigen is critical for the confirmation of E. coli O157:H7;
however, clinical isolates are frequently nonmotile and do not produce
detectable H antigen. To further characterize nonmotile isolates
(designated NM), we developed a PCR-restriction fragment length
polymorphism (PCR-RFLP) test to identify and characterize the gene encoding
the H antigen (fliC) in E. coli. The entire coding sequence of fliC was
amplified by PCR, the amplicon was restricted with RsaI, and the
restriction fragment pattern was examined after gel electrophoresis. Two
hundred eighty E. coli isolates representing serotypes O157:H7 and O157:NM,
flagellar antigen H7 groups associated with other O serogroups, and all
other flagellar antigen groups were analyzed. A single restriction pattern
(pattern A) was identified for O157:H7 isolates, O157:NM isolates that
produced Shiga toxin (formerly Shiga-like toxin or verotoxin), and 16 of 18
O55:H7 isolates. Flagellar antigen group H7 isolates of non-O157 serotypes
had one of three banding patterns distinct from pattern A. A wide variety
of patterns were found among isolates of the other 52 flagellar antigen
groups; however, none was identical to the O157:H7 pattern. Thirteen of 15
nonmotile strains that did not produce the A pattern had patterns that
matched those of other known H groups. The PCR-RFLP in conjunction with O
serogroup determination will be useful in identifying E. coli O157:H7 and
related strains that do not express immunoreactive H antigen and could be
expanded to include other clinically important E. coli strains.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Molecular characterization of the gene encoding H antigen in Escherichia coli and development of a PCR-restriction fragment length polymorphism test for identification of E. coli O157:H7 and O157:NM
Foodborne and Diarrheal Diseases Branch, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA. pif1@cdc.gov
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