Enhancing the antimicrobial properties of silver nanoparticles against ESKAPE bacteria and emerging fungal pathogens by using tea extracts

The sale of antibiotics and antifungals has skyrocketed since 2020. This drives us closer to a silent pandemic of antibiotic resistance. The increasing threat of pathogens like ESKAPE bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), which are effective in evading existing antibiotics, and yeasts like Candida auris or Cryptococcus neoformans is pressing to develop efficient antimicrobial alternatives. Nanoparticles, especially silver nanoparticles (AgNPs), are believed to be promising candidates to supplement or even replace antibiotics in some applications. Here, we propose a way to increase the antimicrobial efficiency of silver nanoparticles by using tea extracts (black, green, or red) for their synthesis. This allows for using lower concentrations of nanoparticles. We found that AgNPs synthesized using green tea extract (G-TeaNPs) are most effective, causing approximately 80% bacterial cell death in Gram-negative bacteria within only 3 hours and at a concentration of 0.1 mg/mL, which is better than antibiotics. Ampicillin at the same concentration (0.1 mg/mL) and within the same duration (3 h) causes only up to 40% decrease in the number of S. aureus and E. cloacae cells (non-resistant strains). Tested silver nanoparticles also have antifungal properties and are effective against C. auris and C. neoformans, which are difficult to eradicate using other means.