Exploring the Antibacterial Potential and Underlying Mechanisms of Prunella vulgaris L. on Methicillin-Resistant Staphylococcus aureus

Abstract

Prunella vulgaris L. (PV) is a widely distributed plant species, known for its versatile applications in both traditional and contemporary medicine, as well as in functional food development. Despite its broad-spectrum antimicrobial utility, the specific mechanism of antibacterial action remains elusive. To fill this knowledge gap, the present study investigated the antibacterial properties of PV extracts against methicillin-resistant Staphylococcus aureus (MRSA) and assessed their mechanistic impact on bacterial cells and cellular functions. The aqueous extract of PV demonstrated greater anti-MRSA activity compared to the ethanolic and methanolic extracts. UPLC-ESI-MS/MS tentatively identified 28 phytochemical components in the aqueous extract of PV. Exposure to an aqueous extract at ½ MIC and MIC for 5 h resulted in a significant release of intracellular nucleic acid (up to 6-fold) and protein (up to 10-fold) into the extracellular environment. Additionally, this treatment caused a notable decline in the activity of several crucial enzymes, including a 41.51% reduction in alkaline phosphatase (AKP), a 45.71% decrease in adenosine triphosphatase (ATPase), and a 48.99% drop in superoxide dismutase (SOD). Furthermore, there was a decrease of 24.17% at ½ MIC and 27.17% at MIC in tricarboxylic acid (TCA) cycle activity and energy transfer. Collectively, these findings indicate that the anti-MRSA properties of PV may stem from its ability to disrupt membrane and cell wall integrity, interfere with enzymatic activity, and impede bacterial cell metabolism and the transmission of information and energy that is essential for bacterial growth, ultimately resulting in bacterial apoptosis. The diverse range of characteristics exhibited by PV positions it as a promising antimicrobial agent with broad applications for enhancing health and improving food safety and quality.

Keywords: MRSA; Prunella vulgaris L.; bacterial metabolism; cell membrane; enzyme activity.

Figure 1

Inhibitory effect of PV aqueous extract at 1/2 MIC and MIC concentrations on MRSA growth over a period of 24 h. Values are represented as mean ± SD of three independent experiments. (** p < 0.01 vs. control).

Figure 2

HPLC-MS negative ion chromatogram of the PV extract.

Figure 3

The effect of the cell membrane permeability and cell wall permeability of MRSA after treatment with PV aqueous extract. (A) The release of 260 nm absorbing materials of MRSA after treatment with PV extract. (B) Protein leakage from MRSA treated with PV aqueous extract at 1/2 MIC and MIC. (C) AKP activity after treatment with PV aqueous extract. Values are expressed as mean ± SD of three independent experiments. (* p < 0.05, ** p < 0.01 vs. Control; ns: not significant).

Figure 4

Effects on ATPase (A) and SOD (B) enzymes in MRSA treated with PV aqueous extract. Results are shown as mean ± SD (* p < 0.05, ** p < 0.01 vs. control, ^$$ p < 0.01, 1/2 MIC group vs. MIC group).

Figure 5

Effects of PV aqueous extracts on MRSA metabolism. Values are means of three independent experiments, expressed as mean ± SD (* p < 0.05 vs. control).

Figure 6

Effects of PV extracts on the total cellular protein. Values are expressed as mean ± SD of three independent experiments. (* p < 0.05 vs. control).