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Applied and Environmental Microbiology, February 2009, p. 1165-1172, Vol. 75, No. 4
0099-2240/09/$08.00+0     doi:10.1128/AEM.01651-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Effect of Molecules Secreted by Lactobacillus acidophilus Strain La-5 on Escherichia coli O157:H7 Colonization{triangledown}

Maira J. Medellin-Peña1,2 and Mansel W. Griffiths2*

Department of Food Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1,1 Canadian Research Institute for Food Safety, Guelph, Ontario, Canada N1G 2W12

Received 17 July 2008/ Accepted 9 December 2008

The probiotic bacterium Lactobacillus acidophilus strain La-5 is a gut-colonizing microorganism that, when established, becomes an important part of the gastrointestinal (GI) tract microbiota. It has been shown to be effective against enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection. We have previously shown that molecules released by probiotic strain La-5 influence the transcription of EHEC genes involved in colonization and quorum sensing. In this work, we report on the ability of these molecules to prevent the adherence of EHEC to epithelial cells and on its capacity to concentrate F-actin at adhesion sites. With a fluorescein-labeled phallotoxin, it was shown that La-5 cell-free spent medium (CFSM) fractions remarkably reduced attaching and effacing lesions in HeLa cells. We also observed a significant inhibition of bacterial adhesion to Hep-2 cells when they were treated with the same La-5 CFSM fractions. In order to observe if La-5 CFSM fractions exhibited the same effect in vivo, we studied the ability of luminescent EHEC constructs (LEE1::luxCDABE) to adhere to intestinal epithelial cells of specific-pathogen-free ICR mice following intragastric inoculation. Colonization of the GI tract by luminescent EHEC O157:H7 was monitored in real time with a slow-scan charge-coupled device camera. At the same time, fecal shedding of EHEC was studied. Following oral gavage of the La-5 active fraction, we observed a reduced amount of bioluminescence signal along with a decrease in fecal shedding by mice, indicating an effect on the ability of the organism to colonize the GI tract. Our results confirm past evidence of the possibility of blocking or interfering with EHEC's virulence by active molecules contained in the probiotic CFSM and identify novel therapeutic alternatives to antibiotic treatments in the fight against food-borne pathogens.

* Corresponding author. Mailing address: Canadian Research Institute for Food Safety, 43 McGilvray St., Guelph, Ontario N1G 2W1, Canada. Phone: (519) 824-4120, ext. 52269. Fax: (519) 763-0952. E-mail: mgriffit{at}uoguelph.ca

{triangledown} Published ahead of print on 16 December 2008.

Applied and Environmental Microbiology, February 2009, p. 1165-1172, Vol. 75, No. 4
0099-2240/09/$08.00+0     doi:10.1128/AEM.01651-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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