Probiotic Lactobacillus salivarius mediated synthesis of silver nanoparticles (AgNPs-LS): A sustainable approach and multifaceted biomedical application

Abstract

Biogenic synthesis of silver nanoparticles (AgNPs) has emerged as an eco-friendly and sustainable approach with diverse biological applications. This study presents synthesis of AgNPs-LS using a probiotic strain Lactobacillus salivarius (L. salivarius) and explores their multifaceted biological activities, including antibacterial, antibiofilm, anti-quorum sensing, antifungal, antioxidant, anticancer, anticoagulant and thrombolytic properties. The biosynthesis of AgNPs-LS was successfully achieved using L. salivarius cell free supernatants, resulting in well-characterized nanoparticles as confirmed by UV-Vis spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) and zeta potential analysis. The AgNPs-LS demonstrated potent antibacterial activity against different pathogenic bacteria (C. violaceum, P. aeruginosa, S. aureus, E. coli and S. marcescens), emphasizing their potential in combating bacterial infections. Moreover, these AgNPs-LS were effective in inhibiting biofilm formation (>60 % at 1/2 MIC), a key mechanism of bacterial virulence, highlighting their utility in preventing biofilm-related infections. AgNPs-LS exhibited anti-quorum sensing activity, disrupting bacterial communication systems and potentially reducing virulence factor such as, violacein production in C. violaceum, pyocyanin production in P. aeruginosa and prodigiosin production in S. marcescens. Additionally, AgNPs-LS also exhibited notable antifungal activity towards a different pathogenic fungus (F. proliferatum, P. purpurogenum, A. niger and R. stolonifer). In terms of health applications, the AgNPs-LS displayed significant antioxidant activity, effectively scavenging DPPH^• (IC₅₀ = 42.65 μg/mL) and ABTS^•+ (IC₅₀ = 53.77 μg/mL) free radicals. Furthermore, AgNPs-LS showed cytotoxicity against breast cancer cells (MCF-7) (IC₅₀ = 52.29 μg/mL), positioning them as promising candidates for cancer therapy. Moreover, AgNPs-LS were also shown promising anticoagulant and thrombolytic activities under practical conditions. Therefore, the biogenic synthesis of AgNPs-LS using L. salivarius offers a sustainable and cost-effective route for producing AgNPs with an array of biological activities. These AgNPs-LS have the potential to address various challenges in healthcare, ranging from antimicrobial, anticancer applications to biofilm inhibition, antioxidant therapy, anticoagulant and thrombolytic agents.

Keywords: Antibiofilm; Antioxidant; Cancer; Lactobacillus salivarius; Silver nanoparticles; TEM.

Graphical abstract

Fig. 1

– Characterization of AgNPs-LS via UV–Vis and FTIR analysis (A). The UV–visible absorption spectra of L. salivarius CFSs, (B). The FTIR analysis of L. salivarius CFSs, (C). UV–Vis absorption spectrum of AgNPs-LS showing the surface plasmon resonance peak, (D). FTIR spectrum of AgNPs-LS indicating the functional groups involved in the synthesis and stabilization of silver nanoparticles.

Fig. 2

– Characterization of AgNPs-LS via DLS, zeta potential and TEM analysis. (A&B). DLS and zeta potential analysis spectrums obtained from AgNPs-LS. The size distribution (maximum intensity at 8.70 nm) and stability (−14.53 mV) of the synthesized AgNPs-LS. (C). The TEM analysis of AgNPs-LS shows the morphology and size range of AgNPs-LS, which are mostly spherical and polyhedral in shape.

Fig. 3

The antibacterial potential of L. salivarius CFSs and AgNPs-LS against different Gram-positive and Gram-negative bacterial pathogens. The results are expressed as the mean ± SD of three replicates. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to Streptomycin.

Fig. 4

The percentage inhibition of biofilm production of different bacterial strains by L. salivarius CFSs and AgNPs-LS (at different sub-MICs). The data are shown as the mean ± SD of three independent experiments. The superscript letters indicate significant differences at p ≤ 0.05 with respect to the control. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to L. salivarius CFSs.

Fig. 5

The percentage inhibition of QS-mediated production of pigments of different bacterial strains by L. salivarius CFSs and AgNPs-LS (at different sub-MICs). (A). The percentage inhibition of violacein production in C. violaceum by L. salivarius CFSs and AgNPs-LS. (B). The percentage inhibition of pyocyanin production in P. aeruginosa by L. salivarius CFSs and AgNPs-LS. (C). The percentage inhibition of prodigiosin production in S. marcescens by L. salivarius CFSs and AgNPs-LS. The data are shown as the mean ± SD of three independent experiments. The superscript letters indicate significant differences at p ≤ 0.05 with respect to the control. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to L. salivarius CFSs.

Fig. 6

Antifungal activity L. salivarius CFSs and AgNPs-LS against different fungal pathogens. The results are expressed as the mean ± SD of three replicates. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to Nystatin.

Fig. 7

Antioxidant activity of L. salivarius CFSs and AgNPs-LS. (A). DPPH^• radical scavenging activity, (B). ABTS^•+ radical scavenging activity. The data are shown as the mean ± SD of three independent experiments. The superscript letters indicate significant differences at p ≤ 0.05 with respect to the control. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to L. salivarius CFSs.

Fig. 8

The effect of L. salivarius CFSs and AgNPs-LS on the viability of MCF-7 breast cancer cells was assessed by MTT assay. The data are shown as the mean ± SD of three independent experiments. The data are shown as the mean ± SD of three independent experiments. Different superscript letters indicate significant differences at p ≤ 0.05 with respect to the control. Significance; ns > 0.05, ∗p < 0.05, ∗∗p < 0.005, ∗∗∗p < 0.0005 with respect to L. salivarius CFSs.

Fig. 9

Anticoagulant and Thrombolytic activity of AgNPs-LS. (A). Control of anticoagulant activity after 60 min (B). Test of anticoagulant activity after 60 min (C). Control of thrombolytic activity (D). Test of thrombolytic activity.