Atomic force microscopy reveals antibacterial mechanisms of Hermetia illucens fatty acids against MDR bacteria.

Acinetobacter baumannii and Staphylococcus aureus are major multidrug-resistant (MDR) pathogens frequently associated with healthcare-acquired infections. The emergence of antimicrobial resistance underscores the urgent need for alternative therapeutics. This study explores the antimicrobial potential of fatty acids (FAs) extracted from Hermetia illucens (HI) larvae fat (AWME3) against MDR strains A. baumannii ATCC 19606 and S. aureus ATCC 55804. AWME3 exhibited potent inhibitory effects, with minimum inhibitory concentrations (MICs) of 0.38 mg/mL for A. baumannii and 0.19 mg/mL for S. aureus. Bactericidal activity occurred within 5-10 min at 0.75 mg/mL. Broth microdilution and propidium iodide uptake assays manifested FA-induced membrane permeabilization (55-70%) within 5 min, supporting a rapid membrane-targeting mechanism. Disruption of membrane integrity was accompanied by significant intracellular ATP depletion, cytoplasmic protein leakage, and altered cellular ultrastructure. AFM imaging showed significant morphological damage, with increased cell surface roughness in both bacterial strains. A. baumannii showed a significant height reduction (51-80%), while S. aureus had a reduction of 26-38% after exposure to 1 × MIC and 2 × MIC. AFM visualizations indicated severe cell envelope damage, including pore formation, blebbing, and surface collapse, consistent with membrane lysis. These findings reveal the swift and membrane-disrupting effects of AWME3 fatty acids on MDR nosocomial pathogens, underscoring their potential as a natural antimicrobial agent. KEY POINTS: • Fatty acids from H. illucens fat show strong activity against MDR pathogens. • Rapid bactericidal effect via membrane disruption and cytoplasmic leakage. • AFM reveals nanoscale cell damage confirming membranolytic action.