Antibacterial activity and antibacterial mechanism of flavaspidic acid BB against Staphylococcus haemelyticus

Abstract

Background: Staphylococcus haemolyticus (S. haemolyticus) is the main etiological factor in skin and soft tissue infections (SSTI). S. haemolyticus infections are an important concern worldwide, especially with the associated biofilms and drug resistance. Herein, we investigated the inhibitory effect of Flavaspidic acid BB obtained from plant extractions on clinical S. haemolyticus strains and their biofilms. Moreover, we predicted its ability to bind to the protein-binding site by molecular simulation. Since the combination of Hsp70 and RNase P synthase after molecular simulation with flavaspidic acid BB is relatively stable, enzyme-linked immunosorbent assay (ELISA) was used to investigate Hsp70 and RNase P synthase to verify the potential antimicrobial targets of flavaspidic acid BB.

Results: The minimum inhibitory concentrations (MIC) of flavaspidic acid BB on 16 clinical strains of S. haemolyticus was 5 ~ 480 µg/mL, and BB had a slightly higher inhibitory effect on the biofilm than MUP. The inhibitory effect of flavaspidic acid BB on biofilm formation was better with an increase in the concentration of BB. Molecular simulation verified its ability to bind to the protein-binding site. The combination of ELISA kits showed that flavaspidic acid BB promoted the activity of Hsp70 and inhibited the activity of RNase P, revealing that flavaspidic acid BB could effectively inhibit the utilization and re-synthesis of protein and tRNA synthesis, thus inhibiting bacterial growth and biofilm formation to a certain extent.

Conclusions: This study could potentially provide a new prospect for the development of flavaspidic acid BB as an antibacterial agent for resistant strains.

Keywords: Anti-bacterial activity; Anti-biofilm activity; Dryopteris fragrans (L.) Schott; Flavaspidic acid BB; Molecular docking; Staphylococcus haemolyticus.

Fig. 1

The effects of different drugs on the biofilm of S. haemolyticus at different growth stages. (A) Biofilm growth curve of S. haemolyticus. (B) Inhibitoin effect of ½MIC-value (10 µg/mL) Flavaspidic acid BB and Mupirocin (1280 µg/mL) on biofilm. (C) Inhibitoin effect of 1MIC-value (20 µg/mL) Flavaspidic acid BB and Mupirocin (2560 µg/mL) on biofilm. (D) Inhibitoin effect of 2MIC-value (40 µg/mL) Flavaspidic acid BB and Mupirocin (5120 µg/mL) on biofilm. *P < 0.05, **P < 0.01, *** P < 0.001 when compared to Mupirocin group

Fig. 2

The characteristics of S. heamolyticus strain biofilms at different timeline (4 h, 8 h, 24 h) from SEM. Magnification: ×3,000

Fig. 3

The characteristics of S. heamolyticus strain biofilms at different timeline (4 h, 8 h, 24 h) under flavaspidic acid BB from SEM. Magnification: ×3,000

Fig. 4

The characteristics of S. heamolyticus strain biofilms at different timeline (4 h, 8 h, 24 h) under MUP from SEM. Magnification: ×3,000

Fig. 5

3D docking conformation of flavaspidic acid BB with five target enzymes: (A) 3D docking conformation of flavaspidic acid BB with ATP synthase; (B) 3D docking conformation of flavaspidic acid BB with eIF2α protein; (C) 3D docking conformation of flavaspidic acid BB with Hsp70 protein; (D) 3D docking conformation of flavaspidic acid BB with NADH dehydrogenase complex I; (E) 3D docking conformation of flavaspidic acid BB with RNase P protein

Fig. 6

Molecular dynamics simulation of flavaspidic acid BB with ATP synthase, eIF2α, Hsp70, NADH-1, RNase P: (A) molecular dynamics simulation of flavaspidic acid BB with ATP synthase; (B) molecular dynamics simulation of flavaspidic acid BB with eIF2α;(C) molecular dynamics simulation of flavaspidic acid BB with Hsp70;(D) molecular dynamics simulation of flavaspidic acid BB with NADH-1;(E) molecular dynamics simulation of flavaspidic acid BB with RNaseP.

Fig. 7

The effects of different drugs on expression of Hsp70 (A) and RNase P (B). *P < 0.05, **P < 0.01 when compared to control group, ^#P < 0.05 when compared to MUP group