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Abstract: As a way to contribute to the assessment of Acinetobacter baumannii clinical population structure, multi-locus sequence typing (MLST) was performed in a collection of 93 isolates from Buenos Aires (1983–2012) and Rosario (2006–2009) hospitals. Sequence types (STs) were achieved by Bartual (B) and Institut Pasteur (P) schemes. PFGE typing, antimicrobial susceptibility assays, and the amplification of the OXA carbapenemase genes most prevalent in our region, were also performed. e-Burst clustered the 25 STsB (15 novels) into 5 clonal complexes (CC) and 5 singletons, and grouped the 18 STsP (12 novels) into 3 CC and 4 singletons. Bartual scheme divided the CC79P into two groups. CC113B/CC79P prevailed in Buenos Aires at least in 1992–2009, being responsible for epidemic and for endemic infections and acquiring the XDR (extensively drug-resistant) pattern throughout the years. While, CC119B/CC79P was apparently present before the CC113B/CC79Pdomain. CC103B/CC15P was the second most prevalent CC. Interestingly, CC110B/ST25P apparently increased over the last years. Conversely, CC109B/CC1P (international clone I) predominated in Rosario, although the presence of CC113B/CC79P, CC103B/CC15P and CC110B/ST25P was observed. Nineteen novel STs clustered in CC79P, CC15P, CC113B, CC109B and CC103B, suggesting their clonal expansion during persistence. PFGE typing proved transmission of strains intra- and inter-hospitals in each city. Except for one, all the recent isolates (2007–2012) harboured the bla OXA-23-like. All isolates were susceptible to colistin. Tigecycline MIC90 was 1mg/L and the rifampicin MIC>512mg/l was found among isolates in three hospitals. In conclusion, the international clone II (CC92B/CC2P) was not found among our isolates. CC113B/CC79P , CC103B/CC15P, and ST25P, suggested also as major components in the A. baumannii population together with the international clone I, were present in Buenos Aires and Rosario with different prevalence rate. Their recent isolates showed high distribution of the bla OXA-23-like as well as the XDR pattern. [Copyright &y& Elsevier]