Objectives: To characterize a highly divergent IMP-type metallo-β-lactamase (MBL) variant detected in a multidrug-resistant Pseudomonas aeruginosa clinical isolate.
Methods: P. aeruginosa isolate 1876 was recovered from an anal swab of an inpatient at a German hospital in the Dutch-German border region (Euregio), where cross-border patient healthcare occurs. MICs were determined by agar dilution and phenotypic screening for MBL production by Etest MBL. Typing was performed by multilocus sequence typing (MLST). PCR assays and nucleotide sequencing were employed for identification of bla gene types. The class 1 integron carrying the blaIMP-type gene was characterized by PCR mapping and sequencing using a set of specific primers. A phylogenetic tree was constructed for the new blaIMP variant.
Results: Isolate 1876 was phenotypically positive for MBL production, exhibited resistance to carbapenems and harboured a new blaIMP-type gene, blaIMP-35. MLST showed that the allelic profile corresponded to ST622, which belongs to the prevalent international clonal complex CC235. The blaIMP-35 gene was located in a class 1 integron as the first gene cassette, followed by blaOXA-35, aacA6, qacEΔ1 and sul1, suggesting its recent integration. IMP-35 was highly divergent, possessing 33/246 (13.4%) different amino acid residues from its closest IMP variants (IMP-8 and IMP-12) and was phylogenetically distinct, representing a separate group in the phylogenetic tree of IMP proteins.
Conclusions: The identification of this phylogenetically distinct IMP-type variant in a CC235 P. aeruginosa suggests the ongoing spread of new IMP-type carbapenemases as well as the potential of the blaIMP-35 gene to evolve in the hospital environment.
Keywords: MBLs; carbapenemases; clusters; divergent; integrons.