Objectives: Emergence of carbapenem-resistant Pseudomonas aeruginosa is limiting current treatment options. Carbapenemases and their association with integrons can cause rapid dissemination of resistance traits. We report here the co-existence and chromosomal inheritance of all four classes of β-lactamase and the presence of a unique class 1 integron (intI1) harbouring blaVIM-5 within a single isolate of P. aeruginosa, DMC-27b.
Methods: DMC-27b, isolated from urine, was characterized for carbapenem resistance both phenotypically and genotypically. The orientation of gene cassette structures of class 1 integrons was determined using referenced and designed overlapping primers and complete genome sequence (CGS) data. The antimicrobial resistance profile, porin protein mutations and the presence of active efflux activity were studied from the CGS.
Results: P. aeruginosa DMC-27b was resistant to a total of 20 antibiotics, with imipenem and meropenem MIC90s of >512 mg/L. The isolate harboured all four classes of β-lactamase: VEB-1 (class A), VIM-5 (class B), PDC-35 (class C) and OXA-2 and OXA-50 (both class D). Chromosomal harbouring of blaVIM-5 was associated with the intI1 gene cassette as the sole gene, a unique cassette so far reported. A total of 11 mutations, among them some mutations causing extra folds and changes in binding sites, in porin protein OprD might also affect its functionality regarding the transportation of antibiotics.
Conclusions: This is one of the earliest reports of its kind on the co-existence of all four β-lactamase classes in P. aeruginosa DMC-27b. Acquisition of multiple resistance determinants is paving the way for the development of MDR. This superbug is a model for rapid dissemination of resistance traits both horizontally and vertically.
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