Zidovudine multi-combos with last-line fosfomycin, ceftazidime-avibactam, colistin and tigecycline against Multi-Drug Resistant Klebsiella pneumoniae

Drug repurposing is a novel strategy for the development of new therapies against antibiotic-resistant bacteria. Zidovudine, an antiviral largely used in the HIV-therapy, exerts antibacterial activity against Gram-negative bacteria. Zidovudine was identified in a previous drug repurposing synergy screening as fosfomycin enhancer against Klebsiella pneumoniae ATCC 13883. Our aim was to evaluate the antibacterial in vitro activity of zidovudine-based combinations with last-line antibiotics against MDR/XDR K. pneumoniae isolates. We validated the zidovudine/fosfomycin combination against a collection of 12 MDR K. pneumoniae isolates by the checkerboard assay (CBA). In addition, we performed time-kill assays (TKA) to analyze synergistic and bactericidal activities of zidovudine paired combinations with fosfomycin, ceftazidime-avibactam, colistin and tigecycline. These were compared with frequent clinical combinations in the treatment of MDR Enterobacteriaceae. The potential of the triple zidovudine/fosfomycin/colistin was also assessed by TKA. CBA synergy confirmation rate between zidovudine/fosfomycin was 83.33%. TKA yielded synergy confirmation rates of 83.3% for zidovudine/ceftazidime-avibactam, 75% for zidovudine/fosfomycin, 75% for zidovudine/colistin and 66.6% for zidovudine/tigecycline with potent killing activities. Frequent clinical combinations displayed synergy rates of 41.6% for meropenem/ertapenem, 33.33% for meropenem/colistin, 75% for fosfomycin/colistin and 66.6% for fosfomycin/tigecycline with lower bactericidal efficacy than zidovudine-based combinations. The triple zidovudine/fosfomycin/colistin combination exhibited activities similar to fosfomycin/colistin and fosfomycin/zidovudine. As conclusion, zidovudine is an effective partner in in vitro combinations with existing antibiotics against MDR K. pneumoniae, especially with ceftazidime-avibactam, fosfomycin or colistin. Further studies are needed to elucidate the clinical potential of zidovudine as a repurposed drug in the antibacterial therapy.