Tn 5406 , a New Staphylococcal Transposon Conferring Resistance to Streptogramin A and Related Compounds Including Dalfopristin

Abstract

We characterized a new transposon, Tn 5406 (5,467 bp), in a clinical isolate of Staphylococcus aureus (BM3327). It carries a variant of vgaA , which encodes a putative ABC protein conferring resistance to streptogramin A but not to mixtures of streptogramins A and B. It also carries three putative genes, the products of which exhibit significant similarities (61 to 73% amino acid identity) to the three transposases of the staphylococcal transposon Tn 554 . Like Tn 554 , Tn 5406 failed to generate target repeats. In BM3327, the single copy of Tn 5406 was inserted into the chromosomal att554 site, which is the preferential insertion site of Tn 554 . In three other independent S. aureus clinical isolates, Tn 5406 was either present as a single plasmid copy (BM3318), as two chromosomal copies (BM3252), or both in the chromosome and on a plasmid (BM3385). The Tn 5406 -carrying plasmids also contain two other genes, vgaB and vatB . The insertion sites of Tn 5406 in BM3252 were studied: one copy was in att554 , and one copy was in the additional SCCmec element. Amplification experiments revealed circular forms of Tn 5406 , indicating that this transposon might be active. To our knowledge, a transposon conferring resistance to streptogramin A and related compounds has not been previously described.