Efficacy of Delafloxacin against the Biothreat Pathogen Burkholderia pseudomallei

Efficacy of ceftazidime in a murine model following a lethal aerosol exposure to Burkholderia pseudomallei

Melioidosis is an endemic disease in numerous tropical regions. Additionally, the bacterium that causes melioidosis, Burkholderia pseudomallei, has potential to be used as a biological weapon. Therefore, development of effective and affordable medical countermeasures to serve regions affected by the disease and to have medical countermeasures available in the event of a bioterrorism attack remains critical. The current study evaluated the efficacy of eight distinct acute phase ceftazidime treatment regimens administered therapeutically in the murine model. At the conclusion of the treatment period, survival rates were significantly greater in several of the treated groups when compared to the control group. Pharmacokinetics of a single dose of ceftazidime were examined at 150 mg/kg, 300 mg/kg, and 600 mg/kg and were compared to an intravenous clinical dose administered at 2000 mg every eight hours. The clinical dose has an estimated 100% fT > 4*MIC which exceeded the highest murine dose of 300 mg/kg every six hours at 87.2% fT > 4*MIC. Based upon survival at the end of the treatment regimen and supplemented by pharmacokinetic modeling, a daily dose of 1200 mg/kg of ceftazidime, administered every 6 h at 300 mg/kg, provides protection in the acute phase of inhalation melioidosis in the murine model.

The BALB/c Mouse Model for the Evaluation of Therapies to Treat Infections with Aerosolized Burkholderia pseudomallei

Burkholderia pseudomallei, the causative agent of the disease melioidosis, has been isolated from the environment in 45 countries. The treatment of melioidosis is complex, requiring lengthy antibiotic regimens, which can result in the relapse of the disease following treatment cessation. It is important that novel therapies to treat infections with B. pseudomallei be assessed in appropriate animal models, and discussions regarding the different protocols used between laboratories are critical. A ‘deep dive’ was held in October 2020 focusing on the use of the BALB/c mouse model and the inhalational route of infection to evaluate new antibiotic therapies.

Efficacy of delafloxacin against the biothreat pathogen Bacillus anthracis

OBJECTIVES

To evaluate the in vitro activity and in vivo efficacy of delafloxacin against Bacillus anthracis, the causative agent of anthrax.

METHODS

MICs were obtained according to CLSI guidelines for 30 virulent isolates and 14 attenuated antibiotic-resistant strains. For the in vivo efficacy study, mice were administered delafloxacin (30-62.5 mg/kg) subcutaneously, or ciprofloxacin (30 mg/kg) intraperitoneally beginning at either 24 or 48 ± 1 h post-challenge (post-exposure prophylaxis) and continued every 12 h for 14 days with study termination on day 30. The mean inhaled dose in the study was approximately 103 × LD50 equivalents, and the range was 87-120 × LD50.

RESULTS

Delafloxacin (MIC90 = 0.004 mg/L) was 16-fold more potent than ciprofloxacin (MIC90 = 0.06 mg/L) against a 30-strain set of virulent B. anthracis. Against a panel of attenuated antibiotic-resistant strains, delafloxacin demonstrated potency ≥128-fold over that observed with ciprofloxacin. When evaluated in vivo, mice treated with all delafloxacin doses tested at 24 h post-challenge demonstrated equivalent survival compared with mice treated with the positive control ciprofloxacin. Because of the high challenge dose of spores, mice treated at 48 h showed rapid and high mortality in all groups including the positive control. Surviving animals in all delafloxacin- and ciprofloxacin-treated groups (24 and 48 h) showed complete splenic clearance of infection and <2.2 × 103 cfu/g lung tissue.

CONCLUSIONS

Given the high bar set by the 100 × LD50 challenge dose in this study, the results from delafloxacin treatment are promising for the treatment of inhaled anthrax.

Evaluation of Delafloxacin against a Burkholderia pseudomallei Efflux Mutant Panel

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.

Biochemical, structural, and computational studies of a γ-carbonic anhydrase from the pathogenic bacterium Burkholderia pseudomallei

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Melioidosis is a severe disease caused Burkholderia pseudomallei.

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γ-carbonic anhydrases (γ-CAs) have been recently introduced as novel antibacterial drug targets.

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A new γ-CA from B. pseudomallei has been investigated by a multidisciplinary approach.

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Obtained results provide an important starting point for developing new anti-melioidosis drugs.

Melioidosis is a severe disease caused by the highly pathogenic gram-negative bacterium Burkholderia pseudomallei. Several studies have highlighted the broad resistance of this pathogen to many antibiotics and pointed out the pivotal importance of improving the pharmacological arsenal against it. Since γ-carbonic anhydrases (γ-CAs) have been recently introduced as potential and novel antibacterial drug targets, in this paper, we report a detailed characterization of BpsγCA, a γ-CA from B. pseudomallei by a multidisciplinary approach. In particular, the enzyme was recombinantly produced and biochemically characterized. Its catalytic activity at different pH values was measured, the crystal structure was determined and theoretical pKa calculations were carried out. Results provided a snapshot of the enzyme active site and dissected the role of residues involved in the catalytic mechanism and ligand recognition. These findings are an important starting point for developing new anti-melioidosis drugs targeting BpsγCA.