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Applied and Environmental Microbiology, October 2008, p. 6032-6040, Vol. 74, No. 19
0099-2240/08/$08.00+0     doi:10.1128/AEM.00991-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Removal of Antibiotic Resistance Gene-Carrying Plasmids from Lactobacillus reuteri ATCC 55730 and Characterization of the Resulting Daughter Strain, L. reuteri DSM 17938

Anna Rosander,^1, Eamonn Connolly,² and Stefan Roos^1*

Department of Microbiology, Swedish University of Agricultural Sciences, P.O. Box 7025, SE-750 07 Uppsala, Sweden,¹ BioGaia AB, P.O. Box 3242, SE-103 64 Stockholm, Sweden²

Received 1 May 2008/ Accepted 4 August 2008

The spread of antibiotic resistance in pathogens is primarily a consequence of the indiscriminate use of antibiotics, but there is concern that food-borne lactic acid bacteria may act as reservoirs of antibiotic resistance genes when distributed in large doses to the gastrointestinal tract. Lactobacillus reuteri ATCC 55730 is a commercially available probiotic strain which has been found to harbor potentially transferable resistance genes. The aims of this study were to define the location and nature of β-lactam, tetracycline, and lincosamide resistance determinants and, if they were found to be acquired, attempt to remove them from the strain by methods that do not genetically modify the organism before subsequently testing whether the probiotic characteristics were retained. No known β-lactam resistance genes was found, but penicillin-binding proteins from ATCC 55730, two additional resistant strains, and three sensitive strains of L. reuteri were sequenced and comparatively analyzed. The β-lactam resistance in ATCC 55730 is probably caused by a number of alterations in the corresponding genes and can be regarded as not transferable. The strain was found to harbor two plasmids carrying tet(W) tetracycline and lnu(A) lincosamide resistance genes, respectively. A new daughter strain, L. reuteri DSM 17938, was derived from ATCC 55730 by removal of the two plasmids, and it was shown to have lost the resistances associated with them. Direct comparison of the parent and daughter strains for a series of in vitro properties and in a human clinical trial confirmed the retained probiotic properties of the daughter strain.

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* Corresponding author. Mailing address: Department of Microbiology, Swedish University of Agricultural Sciences, P.O. Box 7025, SE-750 07 Uppsala, Sweden. Phone: 46 18 67 33 82. Fax: 46 18 67 33 92. E-mail: stefan.roos{at}mikrob.slu.se

Published ahead of print on 8 August 2008.

Present address: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, Box 7009, SE-750 07 Uppsala, Sweden.

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Applied and Environmental Microbiology, October 2008, p. 6032-6040, Vol. 74, No. 19
0099-2240/08/$08.00+0     doi:10.1128/AEM.00991-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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