Process optimization of Syringa oblata Lindl. by response surface methodology and its effect on Staphylococcus xylosus biofilm

Abstract

Syringa oblata Lindl. (S. oblata) is a medicinal plant with effective broad-spectrum antibacterial activity, which can also inhibit Streptococcus suis biofilm formation. The processing of herbal medicine can purify medicinal materials, provide acceptable taste, reduce toxicity, enhance efficacy, influence performance and facilitate preparation. Thus, the aim of this study was to enhance the biofilm inhibition activity of S. oblata toward Staphylococcus xylosus (S. xylosus) using the best processing method. The content of rutin and flavonoids and the ability to inhibit the biofilm formation by S. oblata were examined using four processing methods. One of the best methods, the process of stir-frying S. oblata with vinegar, was optimized based on the best rutin content by response surface methodology. The histidine content and hisB gene expression of S. xylosus biofilm in vitro, resulting from stir-frying S. oblata with vinegar, were evaluated and were found to be significantly decreased and down-regulated, respectively. The results show that S. oblata stir-fried with vinegar can be used to effectively treat diseases resulting from S. xylosus infection. This is because it significantly inhibited S. xylosus biofilm formation by interfering with the biosynthesis of histidine; thus, its mechanism of action is decreasing histidine synthesis.

Fig. 1. The experimental flow chart.

Fig. 2. (A) The rutin content with different Syringa oblata Lindl. processing methods. (B) The total flavonoid content with different Syringa oblata Lindl. processing methods. (C) The inhibition of Staphylococcus xylosus biofilm formation by different Syringa oblata Lindl. processing methods: (a) normal, (b) stir-frying with vinegar, (c) stir-frying with salt-water, (d) stir-frying with ginger juice and (e) stir-frying with honey. Data are expressed as mean ± standard deviation (n = 3). Different letters indicate a significant difference at p < 0.05. (*p < 0.05) is significantly different as compared to the untreated control bacteria.

Fig. 3. Single-factor experiments with the rice vinegar (a) and vinegar (b) (A), and moistening time (B) in the Syringa oblata Lindl. stir-fried with vinegar. Data are expressed as mean ± standard deviation (n = 3).

Fig. 4. Response surface plots (three-dimensional) showing the effects of the moistening time (X₁, min), frying time (X₂, min) and the dosage of vinegar (X₃, mL) on the concentration of rutin (Y₁, μg g⁻¹) and total flavonoids (Y₂, mg g⁻¹) in Syringa oblata Lindl.

Fig. 5. (A) The inhibition of Staphylococcus xylosus biofilm formation by rutin: normal (a) and stir-frying with vinegar (b). (B) Determination of the histidine content and of Staphylococcus xylosus in sub-MICs in the control, normal Syringa oblata Lindl. (a) and Syringa oblata Lindl. stir-fried with vinegar (b). (C) The effect of Syringa oblata Lindl. on the expression of hisB genes in Staphylococcus xylosus. The expression was normalized to that of 16S RNA. Controls refer to the absence of Syringa oblata Lindl. *p < 0.05 and **p < 0.01 as compared to the control bacteria. Different letters indicate a significant difference at p < 0.05. Data are expressed as mean ± standard deviation (n = 3).