Antimicrobial resistance poses a significant global health threat, causing an estimated 1.27 million deaths in 2019. The World Health Organization highlighted this critical issue by publishing its first-ever list of bacterial priority pathogens, designating Acinetobacter baumannii as a Critical-Priority pathogen. This bacterium exhibits resistance to nearly all antibiotics, including last-resort polymyxins. Alarmingly, highly polymyxin-resistant A. baumannii strains with growth defects have emerged in clinical settings, leading to diagnostic and treatment failures.
In this study, we applied a systems pharmacology approach, integrating transcriptomics, metabolomics and lipidomics, to investigate the role of arginine in impacting bacterial membrane integrity in A. baumannii. We found that the arginine degradation pathway was disrupted in the polymyxin-resistant strain Ab5075D (an lpxC mutant) compared to the wild-type Ab5075, with depletion of key metabolites (e.g. L-arginine and L-glutamate) and upregulation of the astCADBE operon. Arginine supplementation in Ab5075D enhanced bacterial metabolic activity, and deleting astA (the first gene in the pathway) restored the composition of membrane phospholipids to wild-type levels.
Using 13C6-arginine as the sole carbon source, stable isotope labelling revealed increased phosphatidylethanolamine (PE) synthesis in Ab5075D, with no significant changes in phosphatidylglycerol. These results suggest that arginine-induced membrane remodelling is driven by enhanced PE synthesis, contributing to membrane stability.
Arginine also significantly enhanced polymyxin killing against key WHO high-priority pathogens, particularly A. baumannii strains, reducing polymyxin minimum inhibitory concentrations by >16-fold. Lipidomics analysis showed that arginine dramatically decreased the phosphoethanolamine modification of lipid A (a key resistance mechanism) by inhibiting the eptA gene in the resistant strain Ab5075R (a pmrB mutant), highlighting its potential to mitigate polymyxin resistance.
Overall, our study provides new insights into how arginine induces membrane remodelling and impacts polymyxin resistance in A. baumannii. It offers a promising therapeutic target to combat antibiotic resistance, representing a groundbreaking opportunity to address life-threatening bacterial infections.