Laboratory of Microbiology and Biologic Assays, Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Via Archirafi, 32, 90123, Palermo, Italy.
Laboratory of Molecular Microbiology and Biotechnology, Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Viale delle Scienze, ed. 16, 90128, Palermo, Italy.
Appl Microbiol Biotechnol. 2020 Jul;104(14):6325-6336. doi: 10.1007/s00253-020-10686-w. Epub 2020 May 27.
Silver nanoparticles (Ag-NPs) can be considered as a cost-effective alternative to antibiotics. In the presence of Fe(III)-citrate and Ag, Klebsiella oxytoca DSM 29614 produces biogenic Ag-NPs embedded in its peculiar exopolysaccharide (EPS). K. oxytoca DSM 29614 was cultivated in a defined growth medium-containing citrate (as sole carbon source) and supplemented with Ag and either low or high Fe(III) concentration. As inferred from elemental analysis, transmission and scanning electron microscopy, Fourier transform infrared spectrometry and dynamic light scattering, Ag-EPS NPs were produced in both conditions and contained also Fe. The production yield of high-Fe/Ag-EPS NPs was 12 times higher than the production yield of low-Fe/Ag-EPS NPs, confirming the stimulatory effect of iron. However, relative Ag content and Ag ion release were higher in low-Fe/Ag-EPS NPs than in high-Fe/Ag-EPS NPs, as revealed by emission-excitation spectra by luminescent spectrometry using a novel ad hoc established phycoerythrin fluorescence-based assay. Interestingly, high and low-Fe/Ag-EPS NPs showed different and growth medium-dependent minimal inhibitory concentrations against Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa ATCC 15442. In addition, low-Fe/Ag-EPS NPs exert inhibition of staphylococcal and pseudomonal biofilm formation, while high-Fe/Ag-EPS NPs inhibits staphylococcal biofilm formation only. Altogether, these results, highlighting the different capability of Ag release, support the idea that Fe/Ag-EPS NPs produced by K. oxytoca DSM 29614 can be considered as promising candidates in the development of specific antibacterial and anti-biofilm agents.Key points • Klebsiella oxytoca DSM 29614 produces bimetal nanoparticles containing Fe and Ag.• Fe concentration in growth medium affects nanoparticle yield and composition.• Phycoerythrin fluorescence-based assay was developed to determine Agrelease.• Antimicrobial efficacy of bimetal nanoparticle parallels Agions release.
银纳米颗粒（Ag-NPs）可以被视为抗生素的一种具有成本效益的替代品。在 Fe(III)-柠檬酸盐和 Ag 的存在下，产酸克雷伯氏菌 DSM 29614 会在其独特的胞外多糖（EPS）中产生生物合成的 Ag-NPs。K. oxytoca DSM 29614 在含有柠檬酸盐（作为唯一碳源）的限定生长培养基中进行培养，并补充 Ag 和低或高 Fe(III)浓度。根据元素分析、透射电子显微镜和扫描电子显微镜、傅里叶变换红外光谱和动态光散射推断，在这两种条件下均产生了 Ag-EPS NPs，且其中还含有 Fe。高 Fe/Ag-EPS NPs 的产量比低 Fe/Ag-EPS NPs 的产量高 12 倍，这证实了铁的刺激作用。然而，通过使用新建立的藻红蛋白荧光测定法的发光光谱的发射-激发光谱，低 Fe/Ag-EPS NPs 中的相对 Ag 含量和 Ag 离子释放量均高于高 Fe/Ag-EPS NPs。有趣的是，高和低 Fe/Ag-EPS NPs 对金黄色葡萄球菌 ATCC 29213 和铜绿假单胞菌 ATCC 15442 的最小抑菌浓度表现出不同的、且依赖于生长培养基的作用。此外，低 Fe/Ag-EPS NPs 可抑制金黄色葡萄球菌和铜绿假单胞菌生物膜的形成，而高 Fe/Ag-EPS NPs 仅抑制金黄色葡萄球菌生物膜的形成。总的来说，这些结果强调了 Ag 释放能力的不同，支持了这样一种观点，即产酸克雷伯氏菌 DSM 29614 产生的 Fe/Ag-EPS NPs 可被视为开发特定抗菌和抗生物膜制剂的有前途的候选物。关键点：
产酸克雷伯氏菌 DSM 29614 产生含有 Fe 和 Ag 的双金属纳米颗粒。
生长培养基中的 Fe 浓度会影响纳米颗粒的产量和组成。
开发了藻红蛋白荧光测定法来确定 Ag 释放。
双金属纳米颗粒的抗菌功效与 Ag 离子的释放相平行。
