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Journal of Clinical Microbiology, September 2003, p. 4285-4291, Vol. 41, No. 9
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.9.4285-4291.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Production of Cytolethal Distending Toxins by Pathogenic Escherichia coli Strains Isolated from Human and Animal Sources: Establishment of the Existence of a New cdt Variant (Type IV)

István Tóth,1 Fréderique Hérault,2 Lothar Beutin,3 and Eric Oswald2*

Veterinary Medical Research Institute of the Hungarian Academy of Sciences, Budapest, Hungary,1 UMR1225, Institut National de la Recherche Agronomique de Microbiologie Moleculaire, Ecole Nationale Vétérinaire de Toulouse, France,2 Division of Emerging Bacterial Pathogens, Robert Koch Institute, Berlin, Germany3

Received 13 December 2002/ Returned for modification 3 February 2003/ Accepted 25 June 2003

Three types of cytolethal distending toxin (CDT), namely, CDT-I, CDT-II, and CDT-III, have been described in Escherichia coli. Using primers designed for the detection of sequences common to the cdtB genes, we analyzed by PCR a set of 21 CDT-producing E. coli strains of intestinal and extraintestinal origins isolated from human and different animal species in several European countries and in the United States. On the basis of the existing differences in the cdtB genes, cdt-I-, cdt-II-, and cdt-III-specific primer pairs were designed and used for cdt typing. These new primers successfully differentiated all of the previously described cdt genes. Six strains proved to be cdt-I; eight strains proved to be cdt-III. However, none of the type I-, II-, and III-specific primers generated amplicons from six CDT+ strains, suggesting the existence of a new cdt variant. Sequence analysis of the amplicons from two untypeable genes confirmed the existence of a new cdt variant that we called cdt-IV. Using the new specific primers, cdt-IV was detected in human, porcine, and poultry strains of intestinal and extraintestinal origins. To validate all sets of cdt specific primers, a group of 353 human E. coli strains isolated in Hungary was then investigated for the presence of cdt genes. This included 190 strains isolated from patients with urinary tract infections (UTI), 51 strains isolated from other (nonurinary) extraintestinal infections, and 112 intestinal strains isolated from healthy individuals. Of 190 UTI strains, 15 (7.9%) had cdt genes. Of 51 non-UTI extraintestinal strains 3 (5.9%) contained the cdt gene, and 1 (0.9%) of 112 healthy intestinal strains was PCR positive. Five strains proved to be cdt-I, and fourteen strains proved to be cdt-IV. The CDT-producing extraintestinal strains belonged to a wide variety of serogroups, including O2, O6, O75, and O170. In conclusion, we have developed a new PCR typing system for CDT able to detect a new CDT variant present in pathogenic E. coli strains obtained from animals and humans.

* Corresponding author. Mailing address: UMR1225 Interactions Hôtes-Agents Pathogènes, Ecole Nationale Vétérinaire de Toulouse, 23 Chemin des Capelles, 31076 Toulouse, France. Phone: 33(0)5-61-19-39-91. Fax: 33(0)5-61-19-39-75. E-mail: e.oswald{at}envt.fr.

Journal of Clinical Microbiology, September 2003, p. 4285-4291, Vol. 41, No. 9
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.9.4285-4291.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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