Clonal Diversity and Resistome Dynamics of Acinetobacter baumannii Isolates from Lithuanian National Cancer Center

<i>Objectives:</i> To investigate the phenotypic and genotypic changes of <i>Acinetobacter baumannii</i> collected from the tertiary oncology setting in Lithuania. <i>Methods:</i><i>A. baumannii</i> isolates (<i>n</i> = 61) were collected in the years 2013-2014 (<i>n</i> = 28) and 2017-2019 (<i>n</i> = 33) from a tertiary care cancer center in Lithuania. Antimicrobial susceptibility was determined according to EUCAST and for piperacillin/tazobactam and cefepime, according to CLSI guidelines. PCR, pulsed-field gel-electrophoresis, and multi-locus sequence typing were used for resistance gene detection and genotyping. The biofilm formation ability was determined by a microtiter plate assay. <i>Results:</i> Of 61 <i>A. baumannii</i> isolates obtained, 84% (51/61) and 71% (43/61) were multi-(MDR) and extensively (XDR) drug-resistant, respectively. Carbapenem-resistant isolates comprised 77% (47/61); of these, 92% (43/47) harbored genes encoding the OXA-23-like, and 4% (2/47) OXA-24-like carbapenemases. All isolates were susceptible to colistin. Genotyping analysis revealed six groups with the highest prevalence of international clones 1 (IC1) and 2 (IC2), which dominated during 2013-2014 and 2017-2019, respectively. Notably, the <i>A. baumannii</i> diversity increased in 2017-2019 with the emergence of 3-LST groups G4, G8, G12, and G14, which included isolates of ST276, ST78, ST1463, and ST1336 sequence types, respectively. The IC1 and IC2 isolates displayed characteristic gene profiles <i>aacC1</i>, <i>aacC2</i>, <i>aphA6</i>, <i>sul1</i>, and <i>armA</i>, <i>strA</i>-<i>strB</i>, <i>bla</i>_TEM, respectively, whereas isolates from other groups had lesser resistance gene content. Isolates from IC2, G12, and G14 groups were strong biofilm producers; IC1, G4, and G8 isolates displayed no/weak biofilm formation capacity. <i>Conclusions:</i><i>A. baumannii</i> from the cancer center showed a high prevalence of MDR and XDR phenotypes. Clonal dominance and diversity changed during the surveillance periods with the replacement of IC1 by IC2 clone isolates and the emergence of higher clonal diversity of isolates with stronger biofilm-forming capacity. The observed changes indicate a concerning trend of the establishment of a more virulent <i>A. baumannii</i> in the cancer setting.