Carbapenem-resistant Pseudomonas aeruginosa carrying bla 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 VITEK2. 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 (ST308) differed from those in isolates harbouring bla (ST277). The mexT gene harboured a mutation resulting in a frameshift in all isolates; in addition, the oprD gene of the bla-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 showed virulence in the G. mellonella model, killing 100% of larvae after 18-24h.

Conclusions: P. aeruginosa carrying bla belonging to ST308 was identified for the first time in our hospital. Although the virulence gene profiles were similar in isolates carrying bla and the isolate carrying bla, only two isolates harbouring bla showed virulence in the G. mellonella model.