An investigation was carried out into the genetic mechanisms responsible for multidrug resistance in nine carbapenem-
resistant Pseudomonas aeruginosa
isolates from different hospitals in Recife, Brazil. Susceptibility to antimicrobial
agents was determined by broth microdilution. Polymerase chain reaction (PCR) was employed to detect
the presence of genes encoding β-lactamases, aminoglycoside-modifying enzymes (AMEs), 16S rRNA methylases,
integron-related genes and OprD. Expression of genes coding for efflux pumps and AmpC cephalosporinase were
assessed by quantitative PCR. The outer membrane proteins were separated by sodium dodecyl sulfate-polyacrylamide
gel electrophoresis. The blaSPM-1
genes were detected in P. aeruginosa
isolates in addition
to different AME genes. The loss of OprD in nine isolates was mainly due to frameshift mutations, premature stop
codons and point mutations. An association of loss of OprD with the overexpression of MexAB-OprM and MexXYOprM
was observed in most isolates. Hyper-production of AmpC was also observed in three isolates. Clonal relationship
of the isolates was determined by repetitive element palindromic-PCR and multilocus sequence typing.
Our results show that the loss of OprD along with overexpression of efflux pumps and β-lactamase production were
responsible for the multidrug resistance in the isolates analysed.