Biological Activity of Propolis – Antimicrobial Activity of Propolis

Antimicrobial Activity of Propolis Extracts
Ethanol is currently the most commonly used solvent for propolis extraction due to its low cost, high extraction efficiency, and the good antimicrobial effect of its extract. Therefore, the ethanol extract of propolis (EEP) is the most common form used in antimicrobial research on propolis. Numerous domestic and international studies have shown that although the sources of propolis may vary, the antimicrobial activity of EEP is similar and its antimicrobial spectrum is very broad. In addition to good antibacterial and antifungal activities, EEP also exhibits certain inhibitory effects against other pathogenic microorganisms (parasites, viruses).

Furthermore, the water extract of propolis (WEP), as well as volatile components obtained through steam distillation, solvent extraction, microwave-assisted extraction, etc., also demonstrate good antimicrobial activity.

Propolis extracts obtained by different methods all exhibit certain antimicrobial effects, although the primary antimicrobial components in these extracts differ, leading to some differences in their antimicrobial mechanisms. However, overall, the antimicrobial effect of the ethanol extract of propolis and the volatile fractions of propolis is significantly higher than that of the water extract.

Factors Influencing the Antimicrobial Activity of Propolis

As a natural product, propolis has abundant sources and a complex composition. The types and content of active components are the material basis for the pharmacological activity of propolis. From collection to extraction and processing, propolis goes through multiple steps and is subject to the influence of various factors, such as botanical origin, collection season, bee species, solvent, extraction temperature, and pH. These factors, to a greater or lesser extent, can affect the types of active components in propolis, the extraction yield, and even the structural stability, ultimately influencing the exertion of its biological activity.

The antimicrobial mechanisms of propolis mainly include the following:

• Disrupting the integrity of the bacterial cell membrane and cell wall, causing the leakage of bacterial contents.
• Inhibiting the formation of bacterial biofilms, affecting bacterial growth and adhesion.
• Inhibiting the activity of bacterial virulence factors and the expression of related genes, reducing their invasiveness and virulence.

The abundant flavonoids and terpenes in propolis play a significant role in exerting its antimicrobial activity. The antimicrobial mechanisms of flavonoids and terpenes mainly include the following (Tim and Lamb, 2011; Zhao Qiang, 2007):

• Damaging the bacterial cell membrane.
• Inhibiting bacterial nucleic acid synthesis.
• Interfering with bacterial energy metabolism.
• Inhibiting bacterial cell wall formation.
• Inhibiting bacterial cell membrane formation.

Active Substances in Propolis against Pathogenic Microorganisms

Propolis has a complex composition, and the main components responsible for its activity vary against different types of microorganisms.
Propolis contains multiple components that have been confirmed to have activity against pathogenic microorganisms, such as pinocembrin, galangin, kaempferol, quercetin, apigenin, caffeic acid phenethyl ester, naringenin, isoferulic acid, caffeic acid, sinapic acid, benzoic acid derivatives, monoterpene and sesquiterpene esters, etc. Furthermore, other components in propolis with reported antimicrobial activity include: pinostrobin, tectochrysin, p-coumaric acid ester, pinobanksin, chrysin, alpinetin, pinobanksin-3-acetate, pinostrobin chalcone, pinocembrin, as well as certain unique active components in specific types of propolis, such as 3-prenyl-4-hydroxycinnamic acid, 2,2-dimethyl-6-carboxyethyl-2H-1-benzopyran (drupanin), 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C), and 2,2-dimethyl-6-carboxyethyl-8-prenyl-2H-1-benzopyran found in Brazilian green propolis (Guo Fangbin, 2004; Yang Shuzhen et al., 2009; Huang Wencheng, 2002).

Reference

Zhao, Q. (2007). Study on the Effective Components of Volatile Oil in Propolis [D]. Master's Thesis, Nanchang University.

Guo, F. B. (2004). The Antibacterial Effect of Propolis [J]. Journal of Bee, (3), 10-12.

Huang, W. C. (2002). Antimicrobial and Antitumor Components in Propolis - Artepillin C [J]. Journal of Bee, (4), 7-8.

Yang, S. Z., Peng, L. T., Yao, X. L., & Pan, S. Y. (2009). Research Progress on the Antifungal Activity of Propolis [J]. Science and Technology of Food Industry, 30(11), 349-352.

Tim Cushniea TP. Lamb AJ (2011) Recent advances in understanding the antibacterial properties of flavonoids [ J ]. International Journal of Antimicrobial Agents, 38 (2): 99-107