A 63 kb genomic resistance island found in a multidrug-resistant Acinetobacter baumannii isolate of European clone I from 1977

Multidrug-resistant Acinetobacter strain HK302 was isolated from an outbreak of nosocomial infections in Switzerland in 1977. The aim of the present study was to assess whether this archive strain belongs to one of the known international clonal lineages of Acinetobacter baumannii and whether it harbours a genomic structure related to the AbaR1-like resistance islands. Multilocus sequence typing (MLST) and HindIII ribotyping were used to determine the taxonomic position of HK302 at the species and subspecies (clonal) levels. The position and structure of the putative resistance island were investigated by AbaR1-based PCR mapping followed by restriction analysis and partial sequencing of amplicons. A. baumannii AYE harbouring AbaR1 was used as a positive control for PCR mapping. The MLST allelic profile (1-1-1-1-5-1-1) and HindIII ribotype of HK302 were typical of A. baumannii European (EU) clone I. In addition, an AbaR1-related region inserted into the ATPase gene at the same position as AbaR1 was found in HK302. PCR mapping and partial sequencing revealed that this region is structurally congruent with AbaR3, a 63.4 kb island described in an A. baumannii isolate from 2004. A. baumannii HK302 belongs to EU clone I and harbours an AbaR3-like island related to resistance islands described in EU clone I strains. Our findings suggest that variants of these sophisticated genomic structures already existed in A. baumannii in the late 1970s.