Mechanisms of resistance were determined in 33 quinolone-resistant isolates of the species Aeromonas hydrophila, Aeromonas caviae, Aeromonas media, Aeromonas salmonicida, Aeromonas popoffii and Aeromonas veronii, recovered from humans, freshwater and eels. The quinolone resistance-determining regions (QRDRs) of gyrA and parC genes were sequenced in these resistant strains, as well as in 8 quinolone-sensitive Aeromonas used as controls. All quinolone-resistant Aeromonas carried point mutations in the gyrA QRDR at codon 83, respectively giving rise to substitutions Ser(83)-->Ile (32 strains) or Ser(83)-->Val (1 strain). Almost half of these isolates (48%) carried additional point mutations in the gyrA QRDR at codon 92 and/or in the parC QRDR at codon 80 corresponding to substitutions Leu(92)-->Met and Ser(80)-->Ile. In all cases, MICs of quinolones were determined in the presence and absence of the efflux pump inhibitor phenylalanine-arginine beta-naphthylamide (PAbetaN). Addition of PAbetaN had no effect on the levels of resistance observed in these isolates. In conclusion, the mechanism of quinolone resistance in the Aeromonas isolates studied was related to mutations in QRDR regions of gyrA and parC genes, with little obvious involvement of pumps inhibited by PAbetaN.
Copyright 2009 Elsevier Masson SAS. All rights reserved.