Two Different Tetracycline Resistance Mechanisms, Plasmid-Carried tet (L) and Chromosomally Located Transposon-Associated tet (M), Coexist in Lactobacillus sakei Rits 9

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 from raw milk, is mediated by a transposon-associated tet(M) gene coding for a ribosomal protection protein and a plasmidcarried tet(L) gene coding for a tetracycline efflux pump. pLS55, the 5-kb plasmid carrying the tet(L) gene, is highly similar to the pMA67 plasmid recently described for Paenibacillus larvae, a species pathogenic to honeybees. pLS55 could be transferred 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 g/ml), L. sakei Rits 9, containing both tetracycline-resistant determinants, had a MIC of <256 g/ml, suggesting that Tet L and Tet M confer different levels of resistance in L. sakei. Remarkably, in the absence of tetracycline, a basal expression of both genes was detected for L. sakei Rits 9. In addition, subinhibitory concentrations of tetracycline affected the expression patterns of tet(M) and tet(L) in different ways: the expression of tet(M) was induced only 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 for the same strain of a lactic acid bacterium.

Characterization of Tetracycline-Resistant Streptococcus thermophilus Isolates from Italian Soft Cheeses

“…To our knowledge, the expression of tetracycline resistance genes in lactic acid bacteria has not been extensively evaluated. Ammor et al (2) found in Lactobacillus sakei an increase in the expression level of tet(M) and tet(L) at higher tetracycline concentrations (up to 64 g ml Ϫ1 ). As the activity of one tetracycline resistance gene, mainly tet(S), can explain the phenotypic resistance observed, we can suppose that in our S. thermophilus strains the expression of the genes tet(M) and tet(L) may be induced as a consequence of a higher concentration of the antibiotic.…”

Detection of a Common and Persistent tet (L)-Carrying Plasmid in Chicken-Waste-Impacted Farm Soil

“…3), reflecting the relatively ancient divergence of this tet(L) gene (39). In pBSDMV46A, pSU1, and pDMV2, a 20-amino-acid putative leader peptide was identified upstream of tet(L), suggesting the possibility of inducible tet(L) expression (4). Apart from tet(L), pBSDMV46A, pSU1, and pDMV2 also contain sequences potentially involved in plasmid replication (rep) and mobilization (mob) (4).…”

Safety Evaluation Of Sjenica Cheese With Regard To Coagulase-Positive Staphylococci And Antibiotic Resistance Of Lactic Acid Bacteria And Staphylococci

“…[74][75][76]. The transmissible nature of tet(M) and tet(K) genes originated from food-borne lactobacilli were confi rmed as it has been shown their association to host a Tn916 transposon [76] and a plasmid [73] respectively.…”

“…The widespread distribution of tet(M) among members of L. plantarum, L. curvatus, L. casei, L. acidophilus, L. gasseri and L. crispatus was reported by several authors [46,71,72]. Ammor et al [73] confi rmed coexistence of two tetracycline resistance genes tet(M) and tet(K) in a foodborne strain of Lactobacillus sakei. Our results did not support this fi nding.…”