# Effect of Biosynthesized Gold and Silver Nanoparticles Using Alchemilla vulgaris Extract and Their Synergistic Action with Subinhibitory Concentrations of Ampicillin Against Staphylococci

## TL;DR

This study explores how gold and silver nanoparticles made from Alchemilla vulgaris can help boost the effectiveness of ampicillin against antibiotic-resistant staphylococci.

## Contribution

The novel contribution is the evaluation of biosynthesized nanoparticles from Alchemilla vulgaris in combination with subinhibitory ampicillin against resistant staphylococci.

## Key findings

- AgNPs-Av and AuNPs-Av inhibited bacterial growth at 50 μg/mL and suppressed biofilm formation at 25 μg/mL.
- AgNPs-Av effectively eradicated biofilm at 50 μg/mL, while AuNPs-Av did not disrupt biofilm.
- Combining nanoparticles with subinhibitory ampicillin showed strong antibacterial and antibiofilm effects (p = 0.001).

## Abstract

Background: Staphylococci, recognized for their virulence and antibiotic resistance, are important in both human and veterinary medicine. Loss of sensitivity to beta-lactam antibiotics, such as ampicillin, complicates therapy, prompting the search for alternative antibacterials or ways to increase drug efficacy. Silver and gold nanoparticles (AgNPs, AuNPs) are promising on their own or in combination with antibiotics. Methods: The aim of this study is to compare the biological activity of pure, washed AgNPs and AuNPs with biosynthesized nanoparticles from Alchemilla vulgaris (AgNPs-Av and AuNPs-Av). Their antibacterial, antibiofilm, and biofilm-eradication effects on the tested antibiotic-resistant, biofilm-forming staphylococci (Methicillin-resistant Staphylococcus aureus (MRSA) and multiresistant Non-aureus staphylococci and mammaliicocci (NASM)) were evaluated using in vitro microdilution methods. Results: AgNPs-Av and AuNPs-Av inhibited bacterial growth at 50 μg/mL, while a significant suppression of biofilm formation was observed at just 25 μg/mL. Our research showed that neither AuNPs-Av nor AuNPs disrupts bacterial biofilm. AgNPs-Av effectively eradicated the biofilm at 50 μg/mL. NPs and ampicillin at subinhibitory antibiotic concentrations against the tested staphylococci. The results showed significant antibacterial and antibiofilm effects (p = 0.001). Partially, biofilm-eradication activity and strong antibiotic potentiation were also detected. Conclusions: These findings highlight the importance of rational combination therapy to improve antibiotic effectiveness and reduce bacterial resistance.