Uptake of ciprofloxacin and ofloxacin by 2 Brucella strains and their fluoroquinolone-resistant variants under different conditions. An in vitro study

The existence of an efflux-mediated mechanism involved in the drug accumulation process of the 2 resistant Brucella strains was investigated; 2 susceptible Brucella strains, Brucella melitensis biovar abortus 2308 (S2308) and AFbortus 3196 (S3196) strains, were the reference strains cultured on trypticase soy agar (TSA) medium and incubated to gradient concentrations of ciprofloxacin and ofloxacin antibiotics. The uptake level of 2 antibacterial agents in 2 susceptible and their fluoroquinolones-resistant variants of Brucella strains obtained in vitro at neutral (pH 7) and acidic (pH 4.5) media, in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP), was analyzed spectrophotometrically. A decreased accumulation was found in all strains at the acidic medium. Accumulation of both ciprofloxacin and ofloxacin was found to be lower in resistant strains than in the susceptible ones. Preincubation with the CCCP had an obvious effect in increased intracellular fluoroquinolone fluorescence. The decrease in drug accumulation seen in 2 resistant Brucella strains could be attributed to an energy-depended efflux mechanism that mediated the resistance to fluoroquinolones, which was often associated with porin alterations (resulting to decreased outer membrane permeability).