New transposon Tn6133 in methicillin-resistant Staphylococcus aureus ST398 contains vga(E), a novel streptogramin A, pleuromutilin, and lincosamide resistance gene

Abstract

A novel streptogramin A, pleuromutilin, and lincosamide resistance determinant, Vga(E), was identified in porcine methicillin-resistant Staphylococcus aureus (MRSA) ST398. The vga(E) gene encoded a 524-amino-acid protein belonging to the ABC transporter family. It was found on a multidrug resistance-conferring transposon, Tn6133, which was comprised of Tn554 with a stably integrated 4,787-bp DNA sequence harboring vga(E). Detection of Tn6133 in several porcine MRSA ST398 isolates and its ability to circularize suggest a potential for dissemination.

Fig. 1.

Comparison of S. aureus transposons Tn554 (GenBank accession no. X03216) and Tn6133 (GenBank accession no. FR772051). Gray areas indicate regions with more than 99% identity between the two transposons. Chromosomal insertion site att554 (K02985) is indicated by gray vertical lines, and the nucleotide repeats at the junction belonging either to the att554 site (left) or the transposon (right) are shown in boxes (DR, direct repeat; IR, inverted repeat). The positions and orientations of open reading frames (ORFs) are represented by arrows. Antibiotic resistance genes ant(9)-Ia, erm(A), and vga(E) (the novel gene; bold) are indicated by black arrows. The gene cluster (orf6133_1 to orf6133_3) encoding two small proteins of unknown function and a new putative serine recombinase (encoded by orf6133_3) are indicated by gray arrows. Genes coding for transposition function (tnpA, tnpB, and tnpC) or unknown function (orf [Tn554] or orf6133_4 [Tn6133]) are indicated by white arrows. Primers used in this study are represented by small black arrows: A, att554-F; B, att554-R; C, tnpA-F; D, orf-R; E, erm(A)-R; F, vga(E)-R4; G, vga(E)-R3; H, vga(E)-F7; I, vga(E)-R; J, tnpA-R; K, vga(E)-F6; L, ant(9)-Ia-R; M, orf6133_3-R8. Cleavage sites for the restriction endonuclease EcoRI are indicated.

Fig. 2.

Relatedness between Vga(E) (bold) and other Vga proteins. The dendrogram was constructed by alignment of the amino acid sequences using BioNumerics 5.10 (Applied Maths) with the following comparison settings: unweighted-pair group method using average linkages (UPGMA); pairwise open gap penalty, 100%; unit gap penalty, 0%; fast algorithm minimum match sequence, 2; maximum number of gaps, 9; gapcost, 0%.