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Infection and Immunity, June 2006, p. 3107-3114, Vol. 74, No. 6
0019-9567/06/$08.00+0     doi:10.1128/IAI.01338-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Significance of Heat-Stable and Heat-Labile Enterotoxins in Porcine Colibacillosis in an Additive Model for Pathogenicity Studies

Weiping Zhang,¹ Emil M. Berberov,² Jessica Freeling,^1, D. He,¹ Rodney A. Moxley,² and David H. Francis^1*

Department of Veterinary Science, South Dakota State University, Brookings, South Dakota,¹ Department of Veterinary and Biomedical Sciences, University of Nebraska—Lincoln, Lincoln, Nebraska²

Received 16 August 2005/ Returned for modification 8 January 2006/ Accepted 15 March 2006

Although heat-stable (ST) and heat-labile (LT) enterotoxins produced by enterotoxigenic Escherichia coli (ETEC) have been documented as important factors associated with diarrheal diseases, investigations assessing the contributions of individual enterotoxins to the pathogenesis of E. coli infection have been limited. To address the individual roles of enterotoxins in the diarrheal disease caused by K88-positive ETEC in young pigs, enterotoxin-positive and -negative isogenic E. coli strains were constructed by using pBR322 to clone and express LT and STb. Four strains, K88⁺ astA, K88⁺ astA/pBR322, K88⁺ astA STb⁺, and K88⁺ astA LT⁺, were constructed and subsequently included in gnotobiotic piglet challenge studies, and their pathogenesis was assessed. The results indicated that all K88⁺ isogenic strains were able to colonize the small intestines of piglets exhibiting the K88 receptor. However, only LT- and STb-positive strains caused appreciable diarrhea. Piglets inoculated with the K88⁺ astA LT⁺ strain became dehydrated within 18 h, while those inoculated with the K88⁺ astA STb⁺ strain did not, although diarrhea developed in several piglets. The changes in the blood packed-cell volume and plasma total protein of gnotobiotic piglets inoculated with the LT-positive strains were significantly greater than those of pigs inoculated with the K88 astA/pBR322 strain (P = 0.012, P = 0.002). Immunochemistry image analysis also suggested that LT enhanced bacterial colonization in a gnotobiotic piglet model. This investigation suggested that LT is a major contributor to the virulence of K88⁺ ETEC and that isogenic constructs are a useful tool for studying the pathogenesis of ETEC infection.

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* Corresponding author. Mailing address: Veterinary Science Department, Box 2157, South Dakota State University, Brookings, SD 57006. Phone: (605) 688-5680. Fax: (605) 688-6003. E-mail: david.francis{at}sdstate.edu.

Journal series contribution 15077 from the University of Nebraska Agricultural Research Division, Lincoln.

Editor: J. F. Urban, Jr.

Present address: Basic Biomedical Sciences, University of South Dakota, Vermillion, SD 57069.

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Infection and Immunity, June 2006, p. 3107-3114, Vol. 74, No. 6
0019-9567/06/$08.00+0     doi:10.1128/IAI.01338-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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