Discovery of broad-spectrum bacterial polyamine detoxification inhibitors as potential antivirulence agents and antibiotic adjuvants

The alarming rise in antimicrobial resistance reinforces an urgent need for new antimicrobial strategies. Chemicals at infection sites, such as polyamines, often influence microbial virulence and antibiotic response. Polyamines are cationic small molecules overproduced by the host during infection, modulating immune responses--the ability of several pathogens to detoxify polyamines correlated with hypervirulence. We sought to uncover inhibitors of polyamine detoxification through a high-throughput whole-cell screen against the community-acquired methicillin-resistant Staphylococcus aureus USA300, identifying the polyamine analog OES2-0017. This inhibitor synergized with polyamines at the low micromolar range, inhibiting a polyamine detoxification spermine/spermidine acetyltransferase SSAT (SpeG) and another previously uncharacterized S. aureus SSAT (denoted PaiASa herein). OES2-0017 showed growth-inhibitory effects at higher concentrations, perturbing the bacterial membrane with no detectable effects against eukaryotic membranes at the same concentration range. OES2-0017 showed similar broad-spectrum activities against various Gram-positive and Gram-negative pathogens. OES2-0017 abolished the polyamine-mediated resistance to antibiotics, including vancomycin, in MRSA USA300, phenocopying the {Delta}speG mutant and suggesting its potential utility as an antibiotic adjuvant. OES2-0017 eradicated SpeG-expressing Salmonella Typhimurium inside murine macrophages, suggesting its potential as an antivirulence agent. Small-scale structure-activity relationship, eukaryotic toxicity, and enzymatic inhibition against the human SSAT (SAT1) assays identified analogs with higher bacterial enzyme specificity and no toxicity at the antimicrobial range. Our screen also uncovered additional inhibitors, including the catechol derivative isoproterenol (OES1-1087), showing a similar mode of action and activity as OES2-0017 but with lower potency. This study provides novel antimicrobial compounds with broad-spectrum activity and a novel mode of action for multidrug-resistant priority pathogens.