Aminoglycoside resistance mechanisms in Pseudomonas aeruginosa isolates from non-cystic fibrosis patients in Thailand

This study aimed to examine aminoglycosides (AMGs) resistance mechanisms, including the AMG-modifying enzyme genes, mexXY, rplY, nuoG, and galU, in the Pseudomonas aeruginosa non-cystic fibrosis (CF) isolates in Thailand. One hundred P. aeruginosa isolates from non-CF patients were examined for susceptibility to AMGs and for the presence of 10 AMG-modifying enzyme genes. Thirty randomly selected isolates were tested for transcription of mexXY and nuoG and mutations in rplY and galU. All the P. aeruginosa isolates exhibited simultaneous resistance to at least 4 AMGs. High resistance rates to amikacin (92%), gentamicin (95%), streptomycin (99%), and tobramycin (96%) were observed, and all isolates were resistant to kanamycin, neomycin, and spectinomycin. Nine AMG-modifying enzyme genes were detected, including aadA1 (84%), aadB (84%), aadA2 (67%), ant(2 '')-Ia (72%), strA-strB (70%), aph(3')-IIb (57%), aac(3')-Ia (40%), and aac(6')-IIa (27%). None of the isolates harbored aac(6')-IIb. Of 30 isolates tested, all but 1 isolate expressed MexXY. Two isolates did not express nuoG. Six isolates carried an amino acid change in RplY, but none of the isolates harbored mutation in galU. The results indicated that the AMG-modifying enzyme genes were widespread among the P. aeruginosa non-CF isolates. The MexXY efflux pump and inactivation for rplY played a role in AMG resistance but disruption of nuoG or galU did not.