Tn6167, an antibiotic resistance island in an Australian carbapenem-resistant Acinetobacter baumannii GC2, ST92 isolate.

OBJECTIVES

To determine the context and location of the bla(OXA-23) carbapenem-resistance gene and the structure of the resistance island in the chromosomal comM gene in a representative Australian global clone 2 (GC2) Acinetobacter baumannii isolate.

METHODS

Long-range PCR was used to link genes and determine the organization of the resistance island. PCR amplicons were sequenced, and bioinformatic analysis identified features. Multilocus sequence typing (MLST) was performed.

RESULTS

The GC2 isolate A91 is sequence type (ST) ST92 (Oxford MLST scheme). It includes a 37 kb genomic resistance island, Tn6167, in the comM gene. At one end, Tn6167 carries Tn6022Δ1 interrupted by a novel insertion sequence, ISAba17. The sul2 (sulphonamide resistance) and strA-strB (streptomycin resistance) genes and tet(B) tetracycline resistance determinant are at the other end in the configuration ISAba1-sul2-CR2Δ-tetA(B)-tetR(B)-CR2-strB-strA with part of the tni end of a Tn6022-related transposon preceding them and an orf4 end following them. Transposon Tn2006 carrying bla(OXA-23) was found in an 11 kb region located between Tn6022Δ1 and the other resistance genes. The 17.6 kb Tn6166 from the GC2 reference strain A320/RUH134 can be derived from Tn6167 via a single deletion arising adjacent to Tn6022Δ1 and causing loss of a large central segment.

CONCLUSIONS

The transposons found in comM in the GC2 isolates A91 and A320 differ substantially from AbaR3-type islands, found predominantly in global clone 1 (GC1) isolates, in both resistance gene content and organization. However, the A. baumannii GC1 and GC2 clones have both acquired antibiotic resistance genes via their association with transposons that target comM.