%0 Journal Article
%A Machuca, Jesus
%A Ortiz, Miriam
%A Recacha, Esther
%A Diaz-De-Alba, Paula
%A Docobo-Perez, Fernando
%A Rodriguez-Martinez, Jose-Manuel
%A Pascual, Alvaro
%T Impact of AAC(6 ')-Ib-cr in combination with chromosomal-mediated mechanisms on clinical quinolone resistance in Escherichia coli
%D 2016
%@ 0305-7453
%U http://hdl.handle.net/10668/18955
%X aac(6')-Ib-cr is the most prevalent plasmid-mediated fluoroquinolone (FQ) resistance mechanism in Enterobacteriaceae. We aimed to analyse the interplay between this plasmid-mediated gene and chromosomal-mediated quinolone resistance mechanisms on both FQ resistance and bacterial fitness in Escherichia coli.E. coli ATCC 25922 and derived isogenic strains carrying chromosomal-mediated quinolone resistance modifications (Ser83Leu-Asp87Asn in GyrA, Ser80Arg in ParC and/or a marR gene deletion) were electroporated with a pBK-CMV vector encoding AAC(6')-Ib-cr. The MICs of FQs were determined by microdilution and bactericidal activity was determined using time-kill curves. A peritoneal sepsis murine model was used to evaluate the in vivo impact. Bacterial fitness was analysed using growth curves and competition assays.The presence of the aac(6')-Ib-cr gene increased the MICs of ciprofloxacin and norfloxacin 4-8-fold for all E. coli genotypes, independently of the initial resistance level. Combination of the aac(6')-Ib-cr gene with three or four chromosomal mechanisms was necessary to reach MIC values above the susceptible category. Killing curve assays showed a clear selective advantage for survival in strains harbouring the aac(6')-Ib-cr gene (up to 7 log(10) cfu/mL after 24 h). AAC(6')-Ib-cr significantly reduced the ciprofloxacin efficacy in vivo. In terms of bacterial fitness cost, maximal OD was significantly lower for all strains harbouring the aac(6')-Ib-cr gene, independently of chromosomal mutations associated.The aac(6')-Ib-cr gene, in spite of producing low-level resistance by itself, plays a relevant role in acquisition of a clinical level of ciprofloxacin and norfloxacin resistance, when combined with three or four chromosomal mutations, both in vitro and in vivo.
%K Determinants qnr
%K Klebsiella-pneumoniae
%K Plasmid
%K Ciprofloxacin
%K Model
%K Spp.
%~