Carbapenem-resistant Pseudomonas aeruginosa carrying bla VIM-36 assigned to ST308: Indicated non-virulence in a Galleria mellonella model.

Objectives: Based on pulsed-field gel electrophoresis (PFGE) profile, whole-genome sequencing (WGS) of eight carbapenem-resistant Pseudomonas aeruginosa isolates from a bone marrow transplant unit in São Paulo, Brazil, was performed to investigate the presence of resistance and virulence genes as well as to determine the sequence type (ST) by multilocus sequence typing (MLST).
Methods: The initial phenotypic susceptibility pattern of the isolates was determined by VITEK ^® 2. Minimum inhibitory concentrations (MICs) were determined by the broth microdilution method for amikacin, meropenem and colistin. WGS was performed using an Illumina MiSeq system. A Galleria mellonella infection model was used to evaluate the virulence of the strains.
Results: WGS demonstrated that mutations in genes encoding outer membrane proteins and efflux pumps in an isolate harbouring bla _VIM-36 (ST308) differed from those in isolates harbouring bla _SPM (ST277). The mexT gene harboured a mutation resulting in a frameshift in all isolates; in addition, the oprD gene of the bla _VIM-36 -carrying isolate had an insertion leading to a frameshift. Virulence genes did not differ between ST277 and ST308 strains. Moreover, only two isolates harbouring bla _SPM showed virulence in the G. mellonella model, killing 100% of larvae after 18-24h.
Conclusions: P. aeruginosa carrying bla _VIM-36 belonging to ST308 was identified for the first time in our hospital. Although the virulence gene profiles were similar in isolates carrying bla _SPM and the isolate carrying bla _VIM-36 , only two isolates harbouring bla _SPM showed virulence in the G. mellonella model.
(Copyright © 2018 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved.)