In vitro activities of delafloxacin and ciprofloxacin were evaluated against Burkholderia pseudomallei mutants expressing or lacking defined resistance-nodulation-cell division (RND) efflux pumps using CLSI methodology at pHs of 5.8 and 7.2. Delafloxacin MIC values were as much as 8-fold lower at pH 5.8 than those at pH 7.2, while ciprofloxacin MICs increased as much as 8-fold. The data from this study suggest that compared to ciprofloxacin, delafloxacin may have improved efflux avoidance, notably at acidic pH. In contrast to ciprofloxacin, delafloxacin may thus retain its therapeutic potential, even in BpeEF-OprC efflux-pump-expressing B. pseudomallei strains that compromise the use of fluoroquinolones, such as ciprofloxacin. IMPORTANCE Resistance-nodulation-cell division (RND) efflux pumps play a major role in intrinsic and acquired antibiotic resistance in Burkholderia pseudomallei, and these pumps are its only known multidrug resistance determinants. Fluoroquinolones have performed poorly in clinical settings and are currently not recommended for treatment of B. pseudomallei infections. While the reasons for the poor clinical performance of this pathogen remain unclear, efflux may be partially responsible since fluoroquinolones like ciprofloxacin are prone to efflux by RND pumps, notably BpeEF-OprC. In vitro efficacy testing using a panel of efflux-proficient and efflux-deficient strains allows identification of fluoroquinolones that compared to ciprofloxacin are less prone to efflux.
Keywords: Burkholderia; biothreat; delafloxacin; efflux pumps; fluoroquinolone.