Diversity of the tetracycline resistance gene tet(M) and identification of Tn916- and Tn5801-like (Tn6014) transposons in Staphylococcus aureus from humans and animals

Objectives: To analyse the sequence diversity of the tetracycline resistance gene tet(M) in Staphylococcus aureus from humans and animals and to determine mobile elements associated with tet(M) in S. aureus. Methods: In total, 205 tetracycline-resistant isolates were screened for tet(M) by PCR. tet(M) genes were sequenced and compared with tet(M) deposited in GenBank. Based on phylogenetic analysis isolates were screened for Tn916- and Tn5801-like xis/int genes, and transposons were confirmed by linking PCR. spa typing was performed and selected isolates were used as donors in a filter mating experiment. Results: Forty-one isolates (21.3%, 60.7%, 2.6% and 4.4% of the human, pig, poultry and cattle isolates, respectively) were tet(M) positive. tet(M) was located on Tn5801-like and Tn916- like transposons in humans and on a specific Tn916- like element in animals. Human isolates were of different spa types (t034, t008, t037, t051, t065, t078, t318 and t964) corresponding to different clonal complexes (CC398, CC8, CC25 and CC30). Animal isolates were of spa type t034, t011 or t0571 corresponding to CC398. tet(M) sequence types correlated with CC types. Tn916- like and Tn5801-like (Tn6014) transposons were able to transfer to S. aureus recipients. Conclusion: S. aureus of human origin contained diverse tet(M) located on Tn916- and Tn5801-like (Tn6014) transposons, and S. aureus of animal origin contained Tn916- like tet(M) genes. This suggests that conjugative transposition plays an important role in the evolution and horizontal spread of tet(M) in S. aureus. This is the first study showing horizontal transfer of Tn5801 (Tn6014).