Evaluation of anti bacteria effects of citrate-reduced silver nanoparticles in Staphylococcus aureus and Escherichia coli

Abstract

Silver nanoparticles (AgNPs) has long known for its inhibitory and bactericidal effects. However, due to its’ attractive antibacterial property, on-going research with various synthesis strategies actively been conducted. In this study, the synthesis of AgNPs was reported, using a simple chemical reduction method with citrate as the reducing agent TEM was used to characterize the obtained AgNPs. Then, Staphylococcus aureus and Escherichia coli were used to identify the antibacterial activity of AgNPs. The inhibition effects of AgNPs against these two bacteria were observed via disc diffusion, and MIC assays and the effects of AgNPs mode of action on both bacteria were further observed under TEM. The formation of AgNPs at ̴ 400 nm, which is the surface plasmon resonance peak was observed using Uv-Vis spectroscopy. The size of AgNPs mostly in the range of 1-10 nm and their morphology appeared to be spherical. Based on the MIC assay, Escherichia coli exhibit low MIC value with 0.049 mg/ml as compared to Staphylococcus aureus with0.391 mg/ml MIC value; correspond to the effective antibacterial activity by the citrate-reduced AgNPs. Further observation on the bacterial surface structure can be seen with cross-sectional TEM image, and it provides an insight into the AgNPs mechanistic aspects of AgNPs against Staphylococcus aureus and Escherichia coli. Silver nanoparticles have been successfully synthesised using the citrate reduction method. Results obtained in this study thus elucidating promising findings to employed AgNPs as an antibacterial agent, and this composition needs to be further study and develop into an antibacterial agent.

Investigation of Nanoparticle Metallic Core Antibacterial Activity: Gold and Silver Nanoparticles against Escherichia coli and Staphylococcus aureus

“…Our results clearly show an antibacterial activity (even low) of AuNPs against E. coli ATCC 25922 and S. aureus ATCC 25923, which strongly differs from recent studies that failed to report any significant antibacterial activity of AuNPs against the same bacterial strains [37,38]. A contrario, for AgNPs, our results seem to be consistent with other studies which found that citrate-capped silver NPs showed a higher activity against E. coli than S. aureus [39][40][41][42]. For example, minimal bactericidal concentrations (MBC) of 9.94 µg/mL (i.e., ≈92 µM of metal) and 19.88 µg/mL (i.e., ≈184 µM) were obtained by C. Quintero-Quiroz et al, for AgNPs (5-50 nm) against E. coli ATCC 25922 and S. aureus ATCC 29213, respectively [40].…”

“…However, with AgNPs of 95.5 nm in diameter (large size distribution) facing the same strains, M. Zarei et al, reported no antibacterial activity against E. coli, while they determined a MIC of 5 µg/mL (i.e., ≈46 µM of metal) against S. aureus [43]. Moreover, 12.9 ± 4.5 nm AgNPs, prepared from silver nitrate, sodium citrate and ascorbic acid, tested against E. coli (MG 1655) and S. aureus (ATCC 6538) led to the determination of MBC of 0.14 mg/mL (i.e., 1.3 µM) and 0.35 mg/mL (3.2 µM) respectively [41]; whereas AgNPs ranging from 1 to 20 nm facing E. coli (ATCC 25922) and S. aureus (ATCC 12600) resulted in MIC of 0.049 mg/mL (i.e., ≈454 µM) and 0.391 mg/mL (i.e., 3625 µM) [42]. The differences observed with our results can be attributed to the AgNPs large size distribution [40,43], the presence of an antibacterial agent in the NPs preparation procedure [41], or the selection of different bacteria strains and concentration range (more specifically when S. aureus is under consideration) [41][42][43].…”

Study of Antibacterial and Anticancer Properties of bioAgNPs Synthesized Using Streptomyces sp. PBD-311B and the Application of bioAgNP-CNC/Alg as an Antibacterial Hydrogel Film against P. aeruginosa USM-AR2 and MRSA

“…Similar conditions were observed in our previous study [45]. The Gram-negative P. aeruginosa cell wall is composed of lipopolysaccharides (LPS) with a highly negative charge that promotes the adhesion of AgNPs [46]. In addition, internalization of bioAgNPs into Gram-negative bacteria is seen as effective due to the different membrane structure.…”