First report of chromosomal co-occurrence of blaAFM-3 and blaIMP-45 genes in a multidrug-resistant Pseudomonas aeruginosa clinical isolate

Background

Multidrug-resistant (MDR) Pseudomonas aeruginosa, especially carbapenemase-producing strains, poses major clinical challenges due to their widespread dissemination and limited treatment options.

Case and Methods

A 65-y-old patient with intracranial infection was hospitalized. An MDR P. aeruginosa strain isolated from her cerebrospinal fluid was analysed using MALDI-TOF mass spectrometry, antimicrobial susceptibility testing, and whole genome sequencing.

Results

P. aeruginosa strain YB1 was resistant to carbapenems, cephalosporins, quinolones, and aminoglycosides, except colistin. Its genome comprised a 6.41-Mb chromosome and a 448-kb IncP-like plasmid. Six β-lactamase genes were identified on the chromosome: bla_PER-1, bla_OXA-1, bla_IMP-45, and bla_AFM-3 in the MDR region, with bla_OXA-488 and bla_PAO-201 located outside it. The chromosomal MDR region shared high homology with plasmid-borne Tn6485e, which originated from multiple plasmids. Specifically, the novel carbapenemase gene bla_AFM-3 resided in a conserved transposon (ISCR27n3-groL-△floR-bla_AFM-3-ble_MBL-trpF-ISCR27n2), identical to that originally characterized in the Alcaligenes faecalis plasmid. Additionally, bla_IMP-45 was located in a conserved type I integron (IntI-aac(6′)-Ib-bla_IMP-45-bla_OXY-1-catB3-△qacE-sul1). Notably, the 3′-terminal sequence of Tn6485e (IS26-aph(3′)-Ia-IS26-tet(C)-tetR(C)-IS26-IS6100), absent from the chromosomal MDR region, was found on YB1’s plasmid. Moreover, IS26 flanked the 71 600-bp chromosomal fragment covering the MRD region, with a 14-bp inverted repeat (5′-GGCACTGTTGCAAA-3′) on their outer sides in the same orientation, implying potential IS26-facilitated plasmid-chromosome recombination.

Conclusions

This study first identified the coexistence of the bla_AFM-3 and bla_IMP-45 genes on the chromosome of P. aeruginosa. Monitoring gene transfer from plasmids to chromosomes is crucial, as it boosts bacterial survival against antibiotics and enables heritable resistance, threatening human health.