Anti-Biofilm and Anti-Hemolysis Activities of 10-Hydroxy-2-decenoic Acid against Staphylococcus aureus

Abstract

Persistent infections caused by Staphylococcus aureus biofilms pose a major threat to global public health. 10-Hydroxy-2-decenoic acid (10-HDA), a main fatty acid in royal jelly, has been shown to possess various biological activities. The purpose of this study was to explore the effects of 10-HDA on the biofilms and virulence of S. aureus and its potential molecular mechanism. Quantitative crystal violet staining indicated that 10-HDA significantly reduced the biofilm biomass at sub-minimum inhibitory concentration (MIC) levels (1/32MIC to 1/2MIC). Scanning electron microscope (SEM) observations demonstrated that 10-HDA inhibited the secretion of extracellular polymeric substances, decreased bacterial adhesion and aggregation, and disrupted biofilm architecture. Moreover, 10-HDA could significantly decrease the biofilm viability and effectively eradicated the mature biofilms. It was also found that the hemolytic activity of S. aureus was significantly inhibited by 10-HDA. qRT-PCR analyses revealed that the expressions of global regulators sarA, agrA, and α-hemolysin gene hla were downregulated by 10-HDA. These results indicate that 10-HDA could be used as a potential natural antimicrobial agent to control the biofilm formation and virulence of S. aureus.

Keywords: 10-hydroxy-2-decenoic acid; Staphylococcus aureus; biofilm; hemolytic activity.

Figure 1

Effect of 10-HDA at sub-MIC levels on the planktonic growth and biofilm biomass of S. aureus. ** p < 0.01.

Figure 2

SEM images (×10,000) of S. aureus biofilms with 10-HDA treatment at the indicated concentrations.

Figure 3

Effect of 10-HDA on bacterial viability during biofilm formation. (A) Effect of 10-HDA on the metabolic activity of the cells in S. aureus biofilms, as analyzed by MTT assay. ** p < 0.01. (B) CLSM images of S. aureus biofilms. Green fluorescence: live cells; red fluorescence: dead cells.

Figure 4

The contents of extracellular (A) polysaccharides, (B) proteins, and (C) eDNA in S. aureus biofilms after 10-HDA treatment. * p < 0.05, ** p < 0.01.

Figure 5

(A) Effect of 10-HDA on S. aureus mature biofilms, as analyzed by crystal violet staining method. (B) MTT assay on the effect of 10-HDA on the cell metabolic activity in S. aureus mature biofilms. * p < 0.05, ** p < 0.01. (C) CLSM images of S. aureus mature biofilms. Green fluorescence: live cells; red fluorescence: dead cells.

Figure 6

Efficacy of 10-HDA in inhibiting the hemolytic activity of S. aureus. (A) Qualitative and (B) quantitative analysis results are shown. ** p < 0.01.

Figure 7

qRT-PCR results of 10-HDA’s effect on the transcription of biofilm- and virulence-related genes. * p < 0.05, ** p < 0.01.