The extensively antibiotic resistant ST111 Acinetobacter baumannii isolate RBH2 carries an extensive mobile element complement of plasmids, transposons and insertion sequences

Abstract

The complete genome of RBH2, a sporadic, carbapenem resistant ST111 Acinetobacter baumannii isolate from Brisbane, Australia was determined and analysed. RBH2 is extensively resistant and the chromosome includes two transposons carrying antibiotic resistance genes, AbaR4 (oxa23 in Tn2006) and Tn7::Tn2006 (dfrA1, sat2, aadA1, oxa23). The chromosome also includes two copies of Tn6175, a transposon carrying putative copper resistance genes, and 1–17 copies of six different insertion sequences. RBH2 has six plasmids ranging in size from 6 kb – 141 kb, four carrying antibiotic resistance genes. Plasmids pRBH2–1 (aadB) and pRBH2–2 (aphA6 in TnaphA6) were found to be essentially identical to known plasmids pRAY*-v1 and pS21–1, respectively. The largest plasmids, pRBH2–5 (oxa23 in AbaR4) and pRBH2–6 (oxa23 in AbaR4::ISAba11 and sul2, tet(B), strA and strB in Tn6172) have known transfer-proficient relatives. pRBH2–5, an RP-T1 (RepAci6) plasmid, also carries a different putative copper resistance transposon related to Tn6177 found in pS21–2. The backbone of pRBH2–5 is related to those of previously described RepAci6 plasmids pAb-G7–2 and pA85–3 but has some distinctive features. Three different RepAci6 backbone types were distinguished, Type 1 (pAb-G7–2), Type 2 (pA85–3) and Type 3 (pRBH2–5 and pS21–2). pRBH2–6 is closely related to pAB3 and their backbones differ by only 5 SNPs. Plasmids pRBH2–3 and pRBH2–4 do not carry antibiotic resistance genes. pRBH2–3 does not include an identifiable rep gene and is a novel plasmid type. pRBH2–4 is of the R3-T3 type and includes segments of the larger pABTJ2 that heads this group. Other ST111 genomes carry different plasmids.