EVOLUTIONARY DYNAMICS AND COMPARATIVE ANALYSIS OF ACINETOBACTER BAUMANNII CLINICAL ISOLATES: INSIGHTS FROM GENOMIC AND PHENOTYPIC APPROACHES

Introduction: Clinical isolates of Acinetobacter baumannii have undergone significant evolutionary pressure due to extensive exposure to stress conditions, particularly with the widespread use of antibiotics. This pressure has led to local clonal expansion and adaptation to various environmental and host factors. Therefore, this study aimed to compare the resistance, virulence, and phenotypic properties of clinical isolates collected over the last decade, employing genomic and phenotypic approaches. Materials and methods: Thirty clinical isolates were obtained from respiratory and urine specimens collected between 2010 and 2023 at a public hospital in Rome. Whole genome sequencing was performed using the Illumina MiSeq platform. Data analysis was conducted using ResFinder, ISfinder, and PlasmidSeeker. Sequence Types (STs) were assigned using the PubMLST Pasteur scheme. Antibiogram and main phenotypic characteristics were also assessed. Results: All isolates belonged to ST2, except one belonging to ST632. Variants of aminoglycoside resistance genes were more prevalent in past respiratory isolates. The blaOXA-23 gene was absent only in two past respiratory isolates. blaOXA-51 and blaADC variants were found in all isolates. blaTEM-1 was detected only in current respiratory isolates, whereas ftsI_A515V was dominant in recent respiratory isolates and in all urine isolates. Genes encoding efflux pumps were found in all isolates. Notably, heavy metal efflux pumps arsC and merE were found only in one past respiratory isolate. ISAba125 was predominant in old respiratory isolates. Strains lacking tsap were not motile. Discussion and conclusion: The recent respiratory isolates exhibited a higher content of antibiotic-resistant and virulence genes. Despite displaying lower MIC values, they were more invasive compared to earlier isolates. These strains showed the highest macrocolony morphology variability. Differently, urinary isolates remained consistent across the different collection times. Investigation of plasmid content is ongoing.