Antimicrobial and anti-biofilm activity of silver nanoparticles biosynthesized with Cystoseira algae extracts

Abstract

Antimicrobial resistance is an ever-growing global concern to public health with no clear or immediate solution. Silver nanoparticles (AgNPs) have long been proposed as efficient agents to fight the growing number of antibiotic-resistant strains. However, the synthesis of these particles is often linked to high costs and the use of toxic, hazardous chemicals, with environmental and health impact. In this study, we successfully produced AgNPs by green synthesis with the aid of the extract of two brown algae—Cystoseira baccata (CB) and Cystoseira tamariscifolia (CT)—and characterized their physico-chemical properties. The NPs produced in both cases (Ag@CB and Ag@CT) present similar sizes, with mean diameters of around 22 nm. The antioxidant activity of the extracts and the NPs was evaluated, with the extracts showing important antioxidant activity. The bacteriostatic and bactericidal properties of both Ag@CB and Ag@CT were tested and compared with gold NPs produced in the same algae extracts as previously reported. AgNPs demonstrated the strongest bacteriostatic and bactericidal properties, at concentrations as low as 2.16 µg/mL against Pseudomonas aeruginosa and Escherichia coli. Finally, the capacity of these samples to prevent the formation of biofilms characteristic of infections with a poorer outcome was assessed, obtaining similar results. This work points towards an alternative for the treatment of bacterial infections, even biofilm-inducing, with the possibility of minimizing the risk of drug resistance, albeit the necessary caution implied using metallic NPs. Graphical abstract

Valorisation of the Invasive Macroalgae Undaria pinnatifida (Harvey) Suringar for the Green Synthesis of Gold and Silver Nanoparticles with Antimicrobial and Antioxidant Potential

“…Nevertheless, some comparisons can be drawn which support the advantages of the nanoparticles included in this study. Comparing the results of the present study with silver and gold nanoparticles produced with extracts of the brown seaweeds Cystoseira tamariscifolia and Cystoseira baccata, the MIC values for the non-biofilm-producing bacteria are at much lower concentrations with the biogenic U. pinnatifida nanoparticles [48]. Other authors reported that silver nanoparticles synthesized in Sargassum wightii (average size 48.78 nm) were toxic to S. aureus at a MIC of 130 µg/mL [49], while particles produced in Turbinaria conoides (up to 80 nm) showed a MIC of 64 and 8 µg/mL against P. aeruginosa and S. aureus, respectively [50].…”

“…On the other hand, no measurable MIC or MBC values were observed for the Au@UP nanoparticles, even at the highest tested concentration of 11.81 µg/mL. Notably, the Ag@UP nanoparticles demonstrated to be even more potent than the antibiotics used as a control (ampicillin and kanamycin; MIC of 40 µg/mL for E. coli and 60 µg/mL for P. aeruginosa and S. aureus), reaching MIC values more than 20 times lower and an average of 5 times lower, compared with silver nitrate (Table 1) [48]. Few reports associate UP extracts with antibacterial activity, which is mostly due to interference of fucoidans with bacterial adhesion to human cells in culture [25].…”

“…The ability of the biosynthesized nanoparticles to inhibit biofilm formation was evaluated using P. aeruginosa PAO1 and S. aureus ATCC 25923 as model microorganisms [48]. While the UP extract had no inhibitory effects, both Ag@UP and Au@UP displayed an inhibitory effect at concentrations lower to the reference antibiotics (Table 2).…”

Antimicrobial Activity of Two Different Types of Silver Nanoparticles against Wide Range of Pathogenic Bacteria

“…It was shown that smaller and round-shaped particles [ 21 ] demonstrate higher antimicrobial activity. Researchers attribute the higher antibacterial activity of these NPs to their greater release of silver ions [ 39 ]. Contrary to expectations, this study found that bigger cube-shaped particles (AgNPs-2) exhibited five times higher antimicrobial effectiveness compared to smaller round-shaped ones (AgNPs-1) against all tested microorganisms.…”

“…Researchers suggest three main mechanisms for the antimicrobial activity of AgNPs such as the formation of reactive oxygen species (ROS), the ion release process, and non-oxidative mechanisms [ 39 ]. The effectiveness of a non-oxidative mechanism or contact killing depends on the contact surface area and surface-to-volume ratio (SA:V).…”