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Journal of Clinical Microbiology, April 2000, p. 1385-1389, Vol. 38, No. 4
Respiratory and Systemic Infection
Laboratory, Central Public Health Laboratory, London NW9 5HT,
United Kingdom
Received 11 August 1999/Returned for modification 3 November
1999/Accepted 17 January 2000
A rapid enzyme immunoassay (EIA) was developed for the phenotypic
detection of diphtheria toxin among clinical isolates of corynebacteria. The assay uses equine polyclonal antitoxin as the
capture antibody and an alkaline phosphatase-labeled monoclonal antibody, specific for fragment A of the toxin molecule, as the detecting antibody. The assay is rapid, sensitive, and specific: a
final result is available within 3 h of colony selection, and the
limits of detection are 0.1 ng of pure diphtheria toxin/ml. Toxigenicity could be detected with isolates grown on a diverse range
of culture media, including selective agars. Toxin detection using the
EIA was compared to that with the Elek test and PCR detection of
fragment A of the diphtheria toxin (tox) gene, using 245 isolates of corynebacteria. The results for the EIA were in complete
concordance with those of the Elek test: 87 toxigenic and 158 nontoxigenic isolates. Ten of the phenotypically nontoxigenic strains
were found to contain fragment A of the tox gene but did not express the toxin protein. These isolates were found to be nontoxigenic in the Vero cell tissue culture cytotoxicity assay and
were therefore nontoxigenic for diagnostic purposes. The EIA is a
simple rapid phenotypic test which provides a definitive result on
toxigenicity within one working day.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Rapid Enzyme Immunoassay for Determination of
Toxigenicity among Clinical Isolates of Corynebacteria
*
Corresponding author. Mailing address: WHO
Collaborating Centre for Diphtheria and Streptococcal Infections,
Respiratory and Systemic Infection Laboratory, Central Public Health
Laboratory, 61 Colindale Ave., London NW9 5HT, United Kingdom. Phone:
44 181 200 4400. Fax: 44 181 205 6528. E-mail:
kengler{at}phls.nhs.uk.
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