In addition, sensitive strain S2 and the CRVs 2X and 2Y did not differ significantly in terms of accumulation of CIP with CCCP. The antioxidant capacity of P. mirabilis determined by FRAP, was significantly higher in CRVs showing greater MICs (1X and 2X), revealing a close correlation between CIP resistance and FRAP (Fig. 3). Lipid oxidation to MDA increased with CIP in both sensitive parental strains and decreased in CRVs (Fig. 4a). Additionally, in absence of antibiotic, MDA was higher in S1, the strain with a lower MIC. Moreover, the Regorafenib oxidization of proteins to carbonyls and AOPP in the presence of CIP increased more

in S1 and S2 than in the CRVs 1X, 1Y, 2X and 2Y (Fig. 4b,c). Table 2 shows that the incorporation of GSH

or AA to culture media reduced the susceptibility of all P. mirabilis CRVs to CIP, as there was an evident increase of MIC in isolates S1, S2 and in all the CRVs after incubation Tamoxifen mw with both antioxidants. The mechanisms involved in the resistance to CIP can be best interpreted by considering the different aspects that may be implicated in the antibacterial mechanism of action. The molecular mechanisms underlying resistance to fluoroquinolones in P. mirabilis include mutations in the target enzymes DNA gyrase and topoisomerase IV (Ser-83 in GyrA, Ser-464 in GyrB and Ser-80 in ParC) and over-expression of endogenous multidrug efflux pumps (Weigel et al., 2002; Saito et al., 2006). Therefore, the

results obtained, indicated that MICs of up to 16 μg mL−1 were displayed in the P. mirabilis CRVs, without typical mutations in DNA gyrase or topoisomerase IV genes. In addition, accumulation studies with CCCP indicated that the influx/efflux mechanisms could contribute to the increase Liothyronine Sodium in the resistance of the CRVs to CIP only in 1X. In this work, an increase in FRAP was proposed as another factor involved in resistance. Previous results of elevated superoxide dismutase and GSH in CRVs (Aiassa et al., 2010) led to the investigation of the antioxidant capacity, as FRAP involves the combined or total reducing power of electron-donating antioxidants (Benzie & Strain, 1996; Litescu et al., 2011). FRAP is also an assay employed in different cellular extracts to measure the antioxidant capacity of different compounds, including antioxidant peptides (Nilsson et al., 2005; Di Bernardini et al., 2011), alpha-lipoic acid and vitamins that can be found in bacteria (Schlesier et al., 2002; Piechota & Goraca, 2009), as validated by several studies (Huang et al., 2005; Thaipong et al., 2006; Magalhães et al., 2008). These antecede even more the investigation of CIP action on biofilm (Aiassa et al., 2007), which indicated that enzymatic and non-enzymatic antioxidant systems may have a role in the defensive reaction against the oxidative stress caused by CIP in P. mirabilis.