Biotechnology and Bioprocess Engineering 2021; 26(4): 650-659  
Biosynthesis of Silver Nanoparticles Using Lavandula stoechas and an Enhancement of Its Antibacterial Activity with Antibiotics
Pei Lin, Zheng-Fei Yan, and Chang-Tian Li
Chang-Tian Li
Engineering Research Center of Edible and Medicinal Fungi, Ministry of Education, Jilin Agricultural University, Changchun 130118, China
Pei Lin
School of Pharmaceutical Sciences, Jiangnan University, Wuxi 214122, China
Zheng-Fei Yan*
State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China
Tel/Fax: +86-0510-85326653
E-mail: zhengfeiyan@jiangnan.edu.cn
Received: December 7, 2020; Revised: January 4, 2021; Accepted: January 10, 2021; Published online: August 30, 2021.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Silver nanoparticles (AgNPs) were successfully synthesized by different extracts of Lavandula stoechas, which have an antibacterial effect on pathogenic strains, such as Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus. Among them, AgNPs-E4 that synthesized by EtOAc extract (E4) have greater antibacterial activity than that by other extracts. The highest inhibition zone diameter (18.6 mm) appeared in C. albicans, at a dosage of 1,000 ppm AgNPs-E4. It was identified as optimal antibacterial AgNPs, which are spherical in shape with an average size at 35.5 nm and maximum absorbance peak at 525 nm. The combined use of penicillin G and AgNPs-E4 exhibited a significant synergistic inhibition effect on the growth of C. albicans, which could produce a maximum inhibition zone of about 21.0 mm. Synergism between antibiotics and AgNPs-E4 was greater than the sum of their individual effects on pathogenic strains. Also, vancomycin, tetracycline, and AgNPs-E4 have slight or no inhibition effect on Escherichia coli. But combined use of the above antibiotics and AgNPs-E4 could exhibit antibacterial activity against E. coli, and the inhibition zone achieved 14.5 and 12.6 mm, respectively, suggesting combined use was able to realize antibacterial effect from nonexistence to pass into existence. HPLC analysis revealed polyphenols were the main compositions of EtOAc extract (E4), such as oleanolic fruit-12-en-3-ol, 19-hydroxyl wusu ester, and lanolin-8-en-3-alcohol. These polyphenols might be particularly useful for the synthesis of antibacterial AgNPs. Therefore, AgNPs synthesized by EtOAc extract of L. stoechas have potential value as antimicrobial agents and also enhance the anti-bacterial activity of antibiotics by combined use.
Keywords: Lavandula stoechas, antibacterial activity, synergistic effect, composition distribution, polyphenols


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