This Article Full Text (PDF) Other Versions of this Article: AEM.01463-07v1 74/5/1394    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ammor, M. S. Articles by Margolles, A. Search for Related Content PubMed PubMed Citation Articles by Ammor, M. S. Articles by Margolles, A. Agricola Articles by Ammor, M. S. Articles by Margolles, A.

 Previous Article  |  Next Article 

Appl. Environ. Microbiol. doi:10.1128/AEM.01463-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Two different tetracycline resistance mechanisms, plasmid-carried tet(L) and chromosomally-encoded transposon-associated tet(M), coexist in Lactobacillus sakei Rits 9

Instituto de Productos Lácteos de Asturias (CSIC), Carretera de Infiesto s/n, 33300 Villaviciosa, Asturias, Spain; Chr. Hansen A/S, Bøge Allé 10-12, 2970 Hørsholm, Denmark; Unité Flore Lactique et Environnement Carné, UR309, INRA, Domaine de Vilvert, F-78350 Jouy-en-Josas, France; RIKILT – Institute of Food Safety, Wageningen UR, Bornsesteeg 45, Wageningen, The Netherlands

^* To whom correspondence should be addressed. Email: amargolles{at}ipla.csic.es.

	Abstract

Lactobacillus sakei is extensively used as functional starter culture in fermented meat products. One of the safety criteria of a starter culture is the absence of potentially transferable antibiotic resistance determinants. However, tetracycline resistant L. sakei strains have already been observed. In this paper, we show that tetracycline resistance in L. sakei Rits 9, a strain isolated from Italian Sola cheese made of raw milk, is mediated by a transposon-associated tet(M) gene, coding for a ribosomal protection protein, and a plasmid-carried tet(L) gene, coding for a tetracycline efflux pump. pLS55, the 5-kb plasmid carrying the tet(L) gene, is highly similar to the plasmid pMA67 recently described in Paenibacillus larvae, a species pathogenic for honey bees. pLS55 could be transfered by electroporation into the laboratory strain L. sakei 23K. While the L. sakei 23K transformant containing pLS55 displayed an intermediate tetracycline resistance level (MIC < 32 µg/ml), L. sakei Rits 9, containing both tetracycline resistant determinants, had a MIC < 256 µg/ml, suggesting that Tet(L) and Tet(M) confer a different level of resistance in L. sakei. Remarkably, in the absence of tetracycline, a basal expression of both genes was detected in L. sakei Rits 9. In addition, subinhibitory concentrations of tetracycline affected the expression patterns of tet(M) and tet(L) in a different way, the expression of tet(M) being only induced at high tetracycline concentrations, whereas the expression of tet(L) was up-regulated at lower concentrations. This is the first time that two different mechanisms conferring resistance to tetracycline are characterized in the same strain of a lactic acid bacterium.