Acinetobacter baumannii appears as an often multidrug-resistant nosocomial pathogen in hospitals worldwide. Its remarkable persistence in the hospital environment is probably due to intrinsic and acquired resistance to disinfectants and antibiotics, tolerance to desiccation stress, capability to form biofilms, and is possibly facilitated by surface-associated motility. Our attempts to elucidate surface-associated motility in A. baumannii revealed a mutant inactivated in a putative DNA-(adenine N6)-methyltransferase, designated A1S_0222 in strain ATCC 17978. We recombinantly produced A1S_0222 as a glutathione 5-transferase (GST) fusion protein and purified it to near homogeneity through a combination of GST affinity chromatography, cation exchange chromatography and PD-10 desalting column. Furthermore we demonstrate A1S0222-dependent adenine methylation at a GAATTC site. We propose the name AamA (Acinetobacter adenine methyltransferase A) in addition to the formal names M.AbaBGORF222P/M.Aba17978ORF8565P. Small angle X-ray scattering (SAXS) revealed that the protein is monomeric and has an extended and likely two-domain shape in solution.