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Infection and Immunity, July 2008, p. 3141-3149, Vol. 76, No. 7
0019-9567/08/$08.00+0     doi:10.1128/IAI.01743-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Comparison of the Contributions of Heat-Labile Enterotoxin and Heat-Stable Enterotoxin b to the Virulence of Enterotoxigenic Escherichia coli in F4ac Receptor-Positive Young Pigs

Joseph Erume,¹ Emil M. Berberov,^1, Stephen D. Kachman,² Michael A. Scott,³ You Zhou,¹ David H. Francis,⁴ and Rodney A. Moxley^1*

Departments of Veterinary & Biomedical Sciences,¹ Statistics, University of Nebraska—Lincoln, Lincoln, Nebraska 68583,² Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, Michigan 48824,³ Department of Veterinary Science, South Dakota State University, Brookings, South Dakota 57007⁴

Received 28 December 2007/ Returned for modification 1 April 2008/ Accepted 11 April 2008

In swine, the most common and severe enterotoxigenic Escherichia coli (ETEC) infections are caused by strains that express K88 (F4)⁺ fimbriae, heat-labile enterotoxin (LT), heat-stable enterotoxin b (STb), and enteroaggregative E. coli heat-stable toxin 1. Previous studies based on a design that involved enterotoxin genes cloned into a nontoxigenic fimbriated strain have suggested that LT but not STb plays an important role in dehydrating diarrheal disease in piglets <1 week old and also enhances bacterial colonization of the intestine. In the present study, we compared these two toxins in terms of importance for piglets >1 week old with a study design that involved construction of isogenic single- and double-deletion mutants and inoculation of 9-day-old F4ac receptor-positive gnotobiotic piglets. Based on the postinoculation percent weight change per h and serum bicarbonate concentrations, the virulence of the STb^– mutant (estB) did not significantly differ from that of the parent. However, deletion of the LT genes (eltAB) in the STb^– mutant resulted in a complete abrogation of weight loss, dehydration, and metabolic acidosis in inoculated pigs, and LT complementation restored the virulence of this strain. These results support the hypothesis that LT is a more significant contributor than STb to the virulence of F4⁺ ETEC infections in young F4ac receptor-positive pigs less than 2 weeks old. However, in contrast to previous studies with gnotobiotic piglets, there was no evidence that the expression of LT enhanced the ability of the F4⁺ ETEC strain to colonize the small intestine.

Published ahead of print on 21 April 2008.

Editor: V. J. DiRita

Present address: Vaccine and Infectious Disease Organization, University of Saskatchewan, 120 Veterinary Road, Saskatoon, Saskatchewan, S7N 5E3 Canada.