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Applied and Environmental Microbiology, May 2008, p. 2679-2689, Vol. 74, No. 9
0099-2240/08/$08.00+0     doi:10.1128/AEM.02286-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Taxonomic and Strain-Specific Identification of the Probiotic Strain Lactobacillus rhamnosus 35 within the Lactobacillus casei Group

Université Clermont 1, UFR Pharmacie, Laboratoire de Bactériologie, Clermont Ferrand, France,¹ CHU de Montpellier, Hôpital Arnaud de Villeneuve, Laboratoire de Bactériologie, Montpellier, France,² Université Montpellier 1, EA 3755, UFR Pharmacie, Laboratoire de Bactériologie, Montpellier, France,³ Université Blaise Pascal, UMR CNRS 6023, Laboratoire de Biologie des Protistes, Aubière, France⁴

Received 8 October 2007/ Accepted 27 February 2008

Lactobacilli are lactic acid bacteria that are widespread in the environment, including the human diet and gastrointestinal tract. Some Lactobacillus strains are regarded as probiotics because they exhibit beneficial health effects on their host. In this study, the long-used probiotic strain Lactobacillus rhamnosus 35 was characterized at a molecular level and compared with seven reference strains from the Lactobacillus casei group. Analysis of rrn operon sequences confirmed that L. rhamnosus 35 indeed belongs to the L. rhamnosus species, and both temporal temperature gradient gel electrophoresis and ribotyping showed that it is closer to the probiotic strain L. rhamnosus ATCC 53103 (also known as L. rhamnosus GG) than to the species type strain. In addition, L. casei ATCC 334 gathered in a coherent cluster with L. paracasei type strains, unlike L. casei ATCC 393, which was closer to L. zeae; this is evidence of the lack of relatedness between the two L. casei strains. Further characterization of the eight strains by pulsed-field gel electrophoresis repetitive DNA element-based PCR identified distinct patterns for each strain, whereas two isolates of L. rhamnosus 35 sampled 40 years apart could not be distinguished. By subtractive hybridization using the L. rhamnosus GG genome as a driver, we were able to isolate five L. rhamnosus 35-specific sequences, including two phage-related ones. The primer pairs designed to amplify these five regions allowed us to develop rapid and highly specific PCR-based identification methods for the probiotic strain L. rhamnosus 35.

Published ahead of print on 7 March 2008.