Antibiotic resistance islands in A320 (RUH134), the reference strain for Acinetobacter baumannii global clone 2

To determine the resistance genes present and the structure of resistance islands in the multiply antibiotic-resistant Acinetobacter baumannii reference strain for global clone 2, RUH134 or A320.

PCR was used to detect antibiotic resistance genes and insertion sequences, and establish linkage between genes. Structures of the resistance islands were determined by PCR mapping and DNA sequencing. Bioinformatic analysis identified features.

A320 carried the strA and strB (streptomycin resistance) genes and the tet(B) tetracycline resistance determinant in a genomic island, Tn6166, located in the chromosomal comM gene. At the left-hand end, Tn6166 carried Tn6022Δ1, a derivative of Tn6022 with a 2.85 kb deletion that removed the tniD gene and part of tniB and tniE. Next to Tn6022Δ1, Tn6166 carried antibiotic resistance genes in the configuration tetA(B)-tetR(B)-CR2-strB-strA and this arrangement was followed by part of the right-hand end of a transposon related to Tn6022 (Tn6021 and Tn6019). The tet(B) determinant is derived from Tn10, but is now located adjacent to the small mobile element CR2. The aacC1 (gentamicin resistance), aadA1 (streptomycin and spectinomycin resistance) and sul1 (sulphonamide resistance) genes were in a class 1 integron, the aphA1 (kanamycin and neomycin resistance), catA1 (chloramphenicol resistance) and bla(TEM) (ampicillin resistance) genes were also detected.

Transposons that target a specific position in comM play an important role in the import of antibiotic resistance genes into members of both of the globally disseminated A. baumannii clones. The organization of the A320/RUH134 island differs from the AbaR3 type.