Antimicrobial activities and low toxicity potential of polyhalogenated phenols against Staphylococcus aureus

Staphylococcus aureus is a common pathogen that acquires antibiotic resistance and often forms biofilm, further reducing its susceptibility to antibiotics. This highlights the need for continuous intervention to combat this threat. In this study, we identified pentabromophenol as a potent antimicrobial agent against S. aureus and selected it for further evaluation. Pentabromophenol exhibited a minimum inhibitory concentration (MIC) of 0.5 µg/mL, superior to conventional antibiotics, ciprofloxacin (1 µg/mL), and tetracycline (2 µg/mL). Additionally, it dose-dependently suppressed biofilm formation and hemolytic activity. Pentabromophenol decreased metabolic activity and cell viability, while it increased N-phenyl-1-naphthylamine (NPN) uptake, indicating enhanced cell membrane permeability. Notably, it demonstrated low propensity for drug resistance with a 4-fold change in MIC over 30 passages compared to over 1000-fold for ciprofloxacin. Importantly, its combination with vancomycin exhibited a marked synergistic effect, lowering the effective dose by 16-fold. Quantitative RT-PCR analysis further revealed the downregulation of genes associated with toxins ( hla and psm-α ), stress response ( sarA and sigB ), and the two-component regulators in S. aureus ( arlR/S ). Toxicity assessments revealed pentabromophenol to be non-toxic to HepG2 liver cells up to 20 µg/mL (40× MIC), Caenorhabditis elegans at concentrations up to 10 µg/mL (20× MIC), and an LD 50 of 270~290 mg/Kg in Sprague-Dawley rats. Taken together, these findings, coupled with its favorable safety profile as determined by ADMET profiling, position pentabromophenol as a promising antimicrobial agent for combating biofilm-associated S. aureus infections. This further highlights that targeted multiple halogenation plays a crucial role in improving the bioactivity of phenols while minimizing their toxic effects. • Pentabromophenol suppressed S . aureus microbial growth and biofilms at ≤0.5 µg/mL. • It inhibited metabolic activity, impaired membrane permeability, and reduced hemolytic activity. • It repressed key genes ( agrA , arlRS, hla , and sarA ) linked to quorum-sensing, antibiotic resistance, virulence, and stress response. • It exhibited low toxicity in plants, nematodes, HepG2 cells, and Sprague-Dawley rats, models. • It showed no resistance development for 30 passages and exhibited strong synergy with vancomycin.