This study aimed to investigate synergistic antibacterial activity of
polymyxin B in combination with the
selective serotonin reuptake inhibitor,
sertraline, against the Gram-negative pathogens Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The combination of
polymyxin B and
sertraline showed synergistic antibacterial activity in checkerboard and static time-kill assays at clinically relevant concentrations against both
polymyxin-susceptible and
polymyxin-resistant isolates. The potential antimicrobial mode of action of the combination was investigated against P. aeruginosa FADDI-PA024 using untargeted metabolomics alongside scanning and transmission electron microscopy (EM). Scanning and transmission EM revealed that the
polymyxin B and
sertraline combination resulted in greater damage to the bacterial cell compared to each drug alone. Metabolomics results showed that the combination significantly affected the bacterial ability to remodel its outer membrane. This was reflected by the major perturbation of
glycerophospholipids and
fatty acids and the pantothenate and
coenzyme A (
CoA) pathways, which feed
fatty acid elongation (e.g., trans-hexadec-2-enoyl-CoA) as well as inhibit the biosynthesis of
lipopolysaccharide and
peptidoglycan. The combination also inhibited the
polymyxin resistance
phosphoethanolamine (pEtN)
lipid A modification pathway, indicated by the declined levels of
phosphoethanolamine. In summary, the present study highlights the potential possibilities of a
polymyxin-
sertraline combination for the treatment of
infections caused by multidrug resistant Gram-negative bacteria such as central nervous system (
CNS) infections via direct intraventricular/intrathecal delivery.