Overcoming an Extremely Drug Resistant (XDR) Pathogen : Avibactam Restores Susceptibility to Ceftazidime for Burkholderia cepacia Complex Isolates from Cystic Fibrosis Patients

Burkholderia multivorans is a significant health threat to persons with cystic fibrosis (CF). Infections are difficult to treat as this pathogen is inherently resistant to multiple antibiotics. Susceptibility testing of isolates obtained from CF respiratory cultures revealed that single agents selected from different antibiotic classes were unable to inhibit growth. However, all isolates were found to be susceptible to ceftazidime when combined with the novel non-β-lactam β-lactamase inhibitor, avibactam (all minimum inhibitor concentrations (MICs) were ≤8 mg/L of ceftazidime and 4 mg/L of avibactam). Furthermore, a major β-lactam resistance determinant expressed in B. multivorans, the class A carbapenemase, PenA was readily inhibited by avibactam with a high k2/K of (2 ± 1) × 10(6) μM(-1) s(-1) and a slow koff of (2 ± 1) × 10(-3) s(-1). Mass spectrometry revealed that avibactam formed a stable complex with PenA for up to 24 h and that avibactam recyclized off of PenA, re-forming the active compound. Crystallographic analysis of PenA-avibactam revealed several interactions that stabilized the acyl-enzyme complex. The deacylation water molecule possessed decreased nucleophilicity, preventing decarbamylation. In addition, the hydrogen-bonding interactions with Lys-73 were suggestive of a protonated state. Thus, Lys-73 was unlikely to abstract a proton from Ser-130 to initiate recyclization. Using Galleria mellonella larvae as a model for infection, ceftazidime-avibactam was shown to significantly (p < 0.001) improve survival of larvae infected with B. multivorans. To further support the translational impact, the ceftazidime-avibactam combination was evaluated using susceptibility testing against other strains of Burkholderia spp. that commonly infect individuals with CF, and 90% of the isolates were susceptible to the combination. In summary, ceftazidime-avibactam may serve as a preferred therapy for people that have CF and develop Burkholderia spp. infections and should be considered for clinical trials.