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Journal of Bacteriology, April 2008, p. 2400-2410, Vol. 190, No. 7
0021-9193/08/$08.00+0     doi:10.1128/JB.00988-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Genetic Diversity of Heat-Labile Toxin Expressed by Enterotoxigenic Escherichia coli Strains Isolated from Humans{triangledown}

M. A. Lasaro,1,{dagger} J. F. Rodrigues,1 C. Mathias-Santos,1 B. E. C. Guth,2 A. Balan,1 M. E. Sbrogio-Almeida,3 and L. C. S. Ferreira1*

Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil,1 Department of Microbiology, Immunology and Parasitology, Federal University of São Paulo, São Paulo, Brazil,2 Division of Technological Development, Butantan Institute, São Paulo, Brazil3

Received 21 June 2007/ Accepted 8 January 2008

The natural diversity of the elt operons, encoding the heat-labile toxin LT-I (LT), carried by enterotoxigenic Escherichia coli (ETEC) strains isolated from humans was investigated. For many years, LT was supposed to be represented by a rather conserved toxin, and one derivative, produced by the reference H10407 strain, was intensively studied either as a virulence factor or as a vaccine adjuvant. Amplicons encompassing the two LT-encoding genes (eltA and eltB) of 51 human-derived ETEC strains, either LT+ (25 strains) only or LT+/ST+ (26 strains), isolated from asymptomatic (24 strains) or diarrheic (27 strains) subjects, were subjected to restriction fragment length polymorphism (RFLP) analysis and DNA sequencing. Seven polymorphic RFLP types of the H10407 strain were detected with six (BsaI, DdeI, HhaI, HincII, HphI, and MspI) restriction enzymes. Additionally, the single-nucleotide polymorphic analysis revealed 50 base changes in the elt operon, including 21 polymorphic sites at eltA and 9 at eltB. Based on the deduced amino acid sequences, 16 LT types were identified, including LT1, expressed by the H10407 strain and 23 other strains belonging to seven different serotypes, and LT2, expressed by 11 strains of six different serotypes. In vitro experiments carried out with purified toxins indicated that no significant differences in GM1-binding affinity could be detected among LT1, LT2, and LT4. However, LT4, but not other toxin types, showed reduced toxic activities measured either in vitro with cultured cells (Y-1 cells) or in vivo in rabbit ligated ileal loops. Collectively, these results indicate that the natural diversity of LTs produced by wild-type ETEC strains isolated from human hosts is considerably larger than previously assumed and may impact the pathogeneses of the strains and the epidemiology of the disease.

* Corresponding author. Mailing address: Departamento de Microbiologia, Universidade de São Paulo, Av. Prof. Lineu Prestes, 1374, Cidade Universitária, São Paulo, Brazil. Phone: 55-11-3091-7338. Fax: 55-11-3091-7354. E-mail: lcsf{at}usp.br

{triangledown} Published ahead of print on 25 January 2008.

{dagger} Present address: Department of Biology, School of Arts and Sciences, University of Pennsylvania, Philadelphia, PA 19104.

Journal of Bacteriology, April 2008, p. 2400-2410, Vol. 190, No. 7
0021-9193/08/$08.00+0     doi:10.1128/JB.00988-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Zhang, C., Rausch, D., Zhang, W. (2009). Little Heterogeneity among Genes Encoding Heat-Labile and Heat-Stable Toxins of Enterotoxigenic Escherichia coli Strains Isolated from Diarrheal Pigs. Appl. Environ. Microbiol. 75: 6402-6405 [Abstract] [Full Text]  


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