Melittin inhibits bacterial growth and reduces biofilm formation across multiple species

Introduction: Biofilms are surface-attached microbial communities encased in an extracellular matrix, creating gradients and metabolic heterogeneity that foster slow-growing, antibiotic-tolerant subpopulations. Predominant in natural and clinical settings, biofilms underlie many chronic and device-related infections. Because standard antibiotics often fail against biofilm-embedded cells, interest has grown in alternatives such as antimicrobial peptides. This study evaluates the antimicrobial and antibiofilm potential of melittin, the main component of honeybee venom. Materials and methods: American Type Culture Collection (ATCC) strains of 14 bacteria were included in this in vitro study. The microdilution method was used to determine minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC), and the crystal violet assay was used to evaluate the impact of melittin on biofilm formation. Results: The MIC of melittin was detected for Staphylococcus aureus and Staphylococcus epidermidis (4 µg/mL), Acinetobacter baumannii and Enterococcus faecalis (4–8 µg/mL), Pseudomonas paraeruginosa and Escherichia coli (32–64 µg/mL), and Klebsiella pneumoniae and Salmonella enterica (128 µg/mL), while Pseudomonas aeruginosa was out of the tested range (>128 µg/mL). Biofilm reduction was observed for P. aeruginosa in two phases, K. pneumoniae at 2 µg/mL, staphylococci at ≥2 µg/mL, and enterococci and Acinetobacter at ≥4 µg/mL. Conclusions: Melittin showed antimicrobial activity against diverse Gram-positive and Gram-negative bacteria, with biofilm reduction associated with growth inhibition in most strains. Melittin appears to be a potential option against resistant bacteria, though its biofilm effects require further study. A key limitation of this study is that most biofilm reductions occurred at or near MIC levels, suggesting that the effect reflects antibacterial killing rather than specific inhibition of biofilm formation. Additionally, the crystal violet assay cannot differentiate viable cells from extracellular matrix or other stained biomass.