Objectives: The aim of the study was to determine whether ATPase genes of genetically diverse Acinetobacter baumannii isolates are disrupted by potential genomic islands.
Methods: Random amplified polymorphic DNA (RAPD)-PCR, sequence grouping and PFGE were used to investigate the genetic diversity of 50 A. baumannii isolated from various clinical specimens. PCR analysis was then used to identify isolates with a potentially disrupted ATPase gene. Representative genetically distinct isolates were further characterized by PCR mapping and chromosome walking to analyse the flanking regions of the disrupted ATPase genes.
Results: Forty-one of the 50 isolates tested appeared to contain a disrupted ATPase gene. Sequence group and PFGE data for 10 ATPase PCR-negative representative isolates confirmed substantial genetic diversity. Seven isolates contained elements with ends showing high levels of sequence similarity to one or both extremities of AbaR1, the first resistance island described in A. baumannii. A further isolate, A25, possessed a highly conserved AbaR1-like 3'-end, but a divergent, though related, 5'-terminus that exhibited near identity with a distinct locus in A. baumannii ATCC 17978. A ninth isolate (A92) possessed a completely novel sequence abutting on its 5'-ATPase remnant. Three isolates appeared to lack 3'-ATPase gene segments, as was the case with the recently sequenced strain ACICU. Thus, 8 of the 10 ATPase-negative isolates investigated in detail had ATPase genes disrupted with AbaR1-like flanking regions.
Conclusions: ATPase genes of diverse A. baumannii isolates are frequently disrupted by insertions matching AbaR1-related flanking sequences. However, the ATPase gene of isolate A92 was disrupted by a DNA sequence distinct from those found in AbaR1.