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Infection and Immunity, May 2006, p. 2906-2916, Vol. 74, No. 5
0019-9567/06/$08.00+0     doi:10.1128/IAI.74.5.2906-2916.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Intestinal Shiga Toxin-Producing Escherichia coli Bacteria Mitigate Bovine Leukemia Virus Infection in Experimentally Infected Sheep

Witold A. Ferens,¹ Rowland Cobbold,^2, and Carolyn J. Hovde^1*

Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, Idaho 83844-3052,¹ Field Disease Investigation Unit, Washington State University, Pullman, Washington 99164-6610²

Received 12 December 2005/ Returned for modification 8 February 2006/ Accepted 22 February 2006

Ruminants often carry gastrointestinal Shiga toxin (Stx)-producing Escherichia coli (STEC). Stxs belong to a large family of ribosome-inactivating proteins (RIPs), found in many plants and some bacteria. Plant RIPs, secreted into extracellular spaces, limit the spread of viruses through plant tissues by penetrating and killing virally infected cells. Previously, we showed Stx activity against bovine leukemia virus (BLV)-infected cells in vitro and hypothesized that STEC bacteria have antiviral activity in ruminant hosts. Here, we investigated the impact of STEC on the initial phases of BLV infection in sheep. Sheep were treated with biweekly oral doses of E. coli O157:H7 (an STEC) or an isogenic stx mutant strain. A different group of sheep were similarly treated with five naturally occurring ovine STEC isolates or stx-negative E. coli. Intestinal STEC bacteria were enumerated and identified by standard fecal culture and DNA hybridization. Oral STEC treatment did not always result in carriage of STEC, although many animals consistently presented with >10⁴ CFU/g feces. BLV viremia was assessed by spontaneous lymphocyte proliferation (SLP) in cultures of blood mononuclear cells and by syncytium formation in cocultures of the same with F-81 indicator cells. SLP was lower (P < 0.05) and syncytia were fewer (P < 0.05) in STEC-treated sheep than in untreated sheep. Both lower SLP and fewer syncytia positively correlated with fecal STEC numbers. Average weight gain post-BLV challenge was higher in STEC-treated sheep than in untreated sheep (P < 0.05). These results support the hypothesis that in ruminants, intestinal STEC bacteria have antiviral activity and mitigate BLV-induced disease.

Editor: A. D. O'Brien

Present address: School of Veterinary Science, University of Queensland, St. Lucia QLD 4072, Australia.

This article has been cited by other articles:

• Cornick, N. A., Helgerson, A. F., Sharma, V. (2007). Shiga Toxin and Shiga Toxin-Encoding Phage Do Not Facilitate Escherichia coli O157:H7 Colonization in Sheep. Appl. Environ. Microbiol. 73: 344-346 [Abstract] [Full Text]