Molecular Bases of Ciprofloxacin Resistance in P. aeruginosa deficient in 8-oxodG Repair System

MORERO NR, ARGARAÑA CE

Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2008

The 8-oxodeoxyguanine (8-oxo-dG) repair system participates in the prevention and correction of mutations generated by oxidative DNA damage in prokaryotes and eukaryotes. We have reported that Pseudomonas aeruginosa strains deficient in this repair mechanism by inactivation of the mutT, mutM or mutY genes show high frequency of resistance to Ciprofloxacin (CP). For the mutT-deficient strain, the CP resistance frequency was increased ~1400-fold over the wild type level, similar to the frequency achieved by the mismatch repair deficient mutS strain. In this work, we show that while all the CP-resistant clones derived from the mutS strain were mutated in GyrA (one of the mayor targets of the drug), the majority of those derived from the mutT strain were only mutated in nfxB, coding for the transcriptional repressor of the efflux pump MexCD-OprJ. The mutations in nfxB were mainly the A>C transversions characteristic of the incorporation of oxidized guanine into DNA, and resulted in important changes in the protein sequence. Finally, we show that CP resistance frequency of wild type and repair deficient strains increased considerably after cell exposure to the oxidizing agent paraquat. Thus, oxidative stress is strongly implicated in the emergence of Ciprofloxacin resistant mutants in P. aeruginosa, and the 8-oxodG repair pathway plays an important role in the prevention of these mutations.