Background: The global rise of multidrug-resistant (MDR) clinical pathogens has created an urgent need for novel antibacterial agents. Green synthesis of silver nanoparticles (Ag NPs) using biological extracts offers an eco-friendly, cost-effective alternative to conventional chemical methods. Insects represent an underexplored but promising biogenic resource due to their high protein and chitin content, low environmental footprint, and established farming infrastructure. The house cricket (Acheta domesticus) is widely farmed as a sustainable protein source but has not been systematically investigated for nanoparticle synthesis.

Objective: To synthesize silver nanoparticles using aqueous extract of house cricket (Acheta domesticus), optimize the synthesis parameters, comprehensively characterize the nanoparticles, and evaluate their antibacterial activity against a panel of clinically relevant multidrug-resistant pathogens.

Methods: Aqueous cricket extract was prepared by boiling crushed adult crickets in deionized water. Ag NPs were synthesized by adding 1 mM silver nitrate to the extract under varying conditions (extract: Ag NO₃ ratio 1:1 to 1:20, pH 3–11, temperature 25–100°C, time 0–120 minutes) to determine optimal parameters. Characterization was performed using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential analysis, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Antibacterial activity was tested against five clinical MDR isolates: methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli, carbapenem-resistant Klebsiella pneumoniae (CR-KP), multidrug-resistant Pseudomonas aeruginosa (MDR-PA), and vancomycin-resistant Enterococcus faecalis (VRE). Activity was assessed by agar well diffusion (zone of inhibition, ZOI) and broth microdilution (minimum inhibitory concentration, MIC, minimum bactericidal concentration, MBC).

Results: Optimal synthesis conditions were established as 1:5 extract: AgNO₃ ratio, pH 8, 60°C, and 60 minutes, yielding a characteristic dark brown color indicative of AgNP formation. UV-Vis spectroscopy confirmed the surface plasmon resonance (SPR) peak at 428 nm. FTIR revealed amide I (1645 → 1628 cm⁻¹) and amide II (1538 → 1520 cm⁻¹) shifts, indicating protein chemisorption as the capping mechanism. XRD confirmed a face-centered cubic crystalline structure with an average crystallite size of 23 nm. DLS showed a Z-average hydrodynamic diameter of 68.4 ± 4.2 nm (polydispersity index 0.214), while TEM revealed predominantly spherical nanoparticles (82%) with a mean primary size of 28.3 ± 6.7 nm (range 15–45 nm). Zeta potential was -32.5 ± 2.8 mV, indicating good colloidal stability. EDX confirmed silver as the major elemental component (73.2 wt%), with carbon, oxygen, and nitrogen from the capping layer.

The AgNPs exhibited concentration-dependent antibacterial activity against all five MDR pathogens. The ZOI at 200 µg/mL ranged from 15.8 mm (VRE) to 21.5 mm (ESBL E. coli). MIC values were 8 µg/mL for ESBL E. coli, 16 µg/mL for MRSA, and 32 µg/mL for CR-KP, MDR-PA, and VRE. MBC values were twice the MIC for all strains (MBC/MIC = 2), confirming bactericidal activity. The cricket extract alone showed no antibacterial activity, confirming that the observed effects are attributable to the nanoparticles.

Conclusion: Acheta domesticus extract is an effective, sustainable reducing and capping agent for the green synthesis of stable, crystalline silver nanoparticles. The cricket-synthesized AgNPs exhibit potent, dose-dependent, bactericidal activity against clinically relevant multidrug-resistant pathogens, including strains resistant to multiple conventional antibiotics. These findings support the potential application of cricket-synthesized AgNPs in topical antimicrobial formulations, wound dressings, and medical device coatings. Further studies are warranted to assess in vivo efficacy, safety, and scalability.