Proteomic profiling and pre-clinical efficacy of antimicrobial lithium complex and colistin combination against multi-drug resistant Acinetobacter baumannii.

Multi-drug resistant (MDR) Acinetobacter baumannii accounts for high mortality rates in hospital-acquired infections. Colistin is the last resort treatment despite nephrotoxic effects and the emergence of colistin resistant A. baumannii is an emerging issue. To tackle this dilemma, metal complexes can be used to potentiate colistin as combination therapy. However, mechanistic and in vivo studies are lacking to present them as compelling therapeutic options. In this study, a lithium complex ([Li(phen)2sal]) based on salicylic acid and 1,10-phenanthroline was used in synergy with colistin to test its antimicrobial and anti-biofilm potential against MDR A. baumannii. Furthermore, proteomics via mass spectrometry, flow cytometry and scanning electron microscopy was performed to study the cellular targets of the treatment. Combination therapy was also tested against pneumonia model in mice to observe pre-clinical efficacy. The lithium complex showed synergistic and additive interaction with colistin and inhibited >85 % of bacterial cells and biofilm formation in A. baumannii strains. Proteomic analysis revealed that combination therapy downregulated significantly more membrane proteins as compared to the individual doses. Flow cytometry indicated that combination therapy caused hyperpolarization in bacteria which led to the cellular damage as observed in scanning electron microscopy. Combination therapy was non-toxic in mice and reduced the clinical score to 0 with bacterial load lessened to 5.56 ± 0.90 log10 CFU in 48 h. Therefore, parenchymal sections had lesser inflammatory regions with intact alveoli. Consequently, combination therapy can be an alternative therapeutic approach with antimicrobial, anti-biofilm, and pre-clinical efficacy against MDR A. baumannii infection.