Agonistic and antagonistic effects of both aqueous and alcoholic extracts of plants containing copper and silver nanoparticles on Escherichia coli and Proteus mirabilis

This study aimed to investigate and compare the inhibitory effects of copper and silver nanoparticles (NPs), as well as aqueous and alcoholic extracts of yarrow and chamomile against E. coli and P. mirabilis bacteria. The extracts were prepared from fresh leaves of chamomile and yarrow plants using the maceration method. Copper NPs were purchased and silver NPs were prepared through the chemical recovery method. The bactericidal effects were measured by changes in the zone of inhibition (ZoI). The absence of a ZoI was interpreted as resistant, <5 mm as semi-sensitive, and >5 mm as sensitive. The results indicated that the NPs had an approximate size of 7 nm. The diameter of the ZoI in aqueous extracts of chamomile and yarrow was greater for E. coli compared to P. mirabilis, while in alcoholic extracts this relationship was reversed. The concentration of 0.4 μg/μL of copper and silver NPs for both bacteria was the most effective concentration of bactericidal NPs. The combined effect of copper NPs and extracts on E. coli and P. mirabilis indicated that the largest ZoI was associated with the alcoholic extract of chamomile (11 mm) and the aqueous extract of yarrow (13 mm), respectively, at a concentration of 0.4 μg/μL of copper NPs. Antagonistic effects of copper NPs on E. coli and P. mirabilis were observed, with an increase in the concentration of copper NPs leading to a larger non-growth halo diameter. The comparison of the bactericidal effects of the extract-nanoparticle combination and the ZoI results of the antibiogram test for 4 antibiotics revealed that the diameter of the ZoI formed by ciprofloxacin was 24 mm for E. coli and 35 mm for P. mirabilis. The difference ZoI of ciprofloxacin on E.coli compared to other antibiotics, as well as the ZoI of chamomile alcoholic extract and yarrow aqueous extract on E. coli and P. mirabilis, was found to be significant (p < 0.05). Furthermore, the minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were observed at a concentration of 500 and 250 μL of the combination of silver NPs + aqueous yarrow extract and the combination of copper NPs + aqueous yarrow extract, respectively. Future research should continue to explore these parameters to develop more effective and sustainable approaches to nanoparticle synthesis.