Genotyping of Acinetobacter baumannii clinical isolates from Polish hospitals uncovers novel sequence types

Acinetobacter baumannii is an opportunistic pathogen associated with healthcare-acquired infections. This study examined the clonal relatedness and drug resistance of 38 clinical isolates of A. baumannii from three hospitals in Poland and five isolates from pig manure. PFGE analysis identified seven clusters (A-G); of these, clusters A and B comprised the majority of clinical isolates, while A and C were dominated by the pig manure isolates, and cluster C included the reference strain ATCC 17978. MLST analysis of the clinical isolates revealed nine sequence types (STs), including three previously-unreported types with a newly-discovered gdhB gene allele. Three new STs were detected in the same hospital. Most isolates belonged to the international clonal complex 2 (IC2), a key contributor to the global spread of A. baumannii. Alarmingly, while all isolates from pig manure remained susceptible to the tested antibiotics, over 97.3% of clinical isolates were classified as extensively drug-resistant (XDR). Detection of β-lactamase-encoding genes by targeted PCR revealed nearly ubiquitous presence of blaOXA- among the clinical samples (97%), with blaOXA-23 (43%) as the predominant acquired carbapenemase gene; blaOXA-40, blaOXA-58, and blaTEM were observed less frequently. Our findings emphasise the genetic diversity of A. baumannii in clinical environments and reveal previously unreported STs among XDR clinical isolates; they also reinforce the need for improved infection surveillance and control to combat the spread of multidrug-resistant (MDR) and XDR strains.