Identification of tet(M) in two Lactococcus lactis strains isolated from a Spanish traditional starter-free cheese made of raw milk and conjugative transfer of tetracycline resistance to lactococci and enterococci.
Specific PCR and sequencing showed that a tet(M) gene was present in two tetracycline-resistant Lactococcus lactis strains isolated from a raw milk, starter-free cheese. Hybridisation experiments using as a probe an internal segment of the gene obtained by PCR associated tet(M) with plasmids of around the same size (30 kbp) in both strains. Molecular analysis of the tetracycline resistance loci, including the upstream and downstream regions of the genes, showed them to be identical to one other and to the tet(M) encoded by the conjugative transposon Tn916. Amplification of Tn916-derived segments suggested the transposon was complete in the two L. lactis strains. Further, curing of the tetracycline resistance was accompanied by a reduction in size of the plasmids comparable to that expected for Tn916. Tetracycline resistance could be transferred by conjugation to plasmid-free Lactococcus and Enterococcus strains. However, no plasmid DNA was detected among the transconjugants while both tet(M) and transposon-related sequences were amplified by PCR. This suggested that only the transposon was mobilized.
Flórez
Ana Belén
AB
Instituto de Productos Lácteos de Asturias (CSIC), Carretera de Infiesto s/n, 33300-Villaviciosa, Asturias, Spain.
Ammor
Mohammed Salim
MS
Mayo
Baltasar
B
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002611:Cheese / Q000382:microbiology; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics; D016983:Enterococcus / Q000187:drug effects / Q000235:genetics; D005516:Food Microbiology; D005784:Gene Amplification; D005798:Genes, Bacterial; D017045:Lactococcus / Q000187:drug effects / Q000235:genetics; D013294:Lactococcus lactis / Q000187:drug effects* / Q000235:genetics*; D008892:Milk / Q000382:microbiology*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D013752:Tetracycline; D013753:Tetracycline Resistance / Q000235:genetics*
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C083138:Tet M resistance protein, Bacteria; D013752:Tetracycline