Genomic Insights into Vietnamese Extended-Spectrum β-Lactamase-9-Producing Extensively Drug-Resistant Pseudomonas aeruginosa Isolates Belonging to the High-Risk Clone ST357 Obtained from Bulgarian Intensive Care Unit Patients

Extensively drug-resistant <i>P. aeruginosa</i> (XDR-PA) has been highlighted as a serious public health threat. The present study aimed to explore the genomic characteristics of two Vietnamese extended-spectrum β-lactamase-9 (VEB-9)-producing XDR-PA isolates from Bulgaria in comparison to all <i>bla</i>_VEB-9-positive strains with available genomes. The isolates designated Pae51 and Pae52 were obtained from tracheobronchial aspirates of intensive care unit (ICU) patients. Antimicrobial susceptibility testing, whole-genome sequencing, RT-qPCR, and phylogenomic analysis were performed. Pae51 and Pae52 were resistant to most antipseudomonal β-lactams including carbapenems, aminoglycosides, and fluoroquinolones but remained susceptible to colistin and cefiderocol. Numerous resistance determinants were detected: <i>bla</i>_VEB-9, <i>bla</i>_PDC-3, <i>bla</i>_OXA-10, <i>bla</i>_OXA-50, <i>aac(6')-II</i>, <i>ant(2″)-Ia</i>, <i>ant(3″)-IIa</i>, <i>aph(3')-IIb</i>, <i>cprP</i>, <i>catB7</i>, <i>dfrB2</i>, <i>sul1</i>, <i>fosA</i>, and <i>tet(A)</i>. Both isolates carried complex integrons with <i>bla</i>_VEB-9 and <i>tet(A)</i> embedded next to the conservative 3' end sequences. A variety of virulence factors were also identified, including the type III secretion system exotoxin U. Pae51 and Pae52 differed by only four SNPs and belonged to the high-risk clone ST357. To our knowledge, this is the first report of <i>bla</i>_VEB-9-positive XDR-PA isolates in Bulgaria presenting a detailed genomic analysis. The development of novel antimicrobial strategies for such pathogens should be an essential part of infection control stewardship practices in ICU wards.