Antimicrobial activity of D-amino acid in combination with photo-sonoactivated hypericin nanoparticles against Acinetobacter baumannii

Abstract

Background: The emergence of multidrug-resistant Acinetobacter baumannii strains is increasing worldwide. To overcome these life-threatening infections, the development of new treatment approaches is critical. For this purpose, this study was conducted to determine the antimicrobial photo-sonodynamic therapy (aPSDT) using hypericin nanoparticles (HypNP) in combination with D-Tryptophan (D-Trp) against A. baumannii.

Materials and methods: HypNP was synthesized and characterized, followed by the determination of the fractional inhibitory concentration (FIC) index of HypNP and D-Trp by checkerboard assay. Next, the antimicrobial and anti-biofilm potential of HypNP@D-Trp-mediated aPSDT against A. baumannii was evaluated. Finally, the anti-virulence activity of aPSDT using HypNP@D-Trp was accessed following the characterization of HypNP@D-Trp interaction with AbaI using in silico virtual screening and molecular docking.

Results: A synergistic activity in the combination of HypNP and D-Trp against A. baumannii was observed with a FIC index value of 0.5. There was a 5.10 log₁₀ CFU/mL reduction in the cell viability of A. baumannii when the bacterial cells were treated with 1/2 × MIC of HypNP@D-Trp and subsequently exposed to ultrasound waves and blue light (P < 0.05). Moreover, a significant biofilm degradation effect on biofilm-associated cells of A. baumannii was observed after treatment with aPSDT using 2 × MIC of HypNP@D-Trp in comparison with the control groups (P < 0.05). According to the molecular docking analysis of the protein-ligand complex, Hyp with a high affinity for AbaI showed a binding affinity of - 9.41 kcal/mol. Also, the expression level of abaI gene was significantly downregulated by 10.32-fold in A. baumannii treated with aPSDT as comprised with the control group (P < 0.05).

Conclusions: It can be concluded that HypNP@D-Trp-mediated aPSDT can be considered a promising strategy to overcome the infections caused by A. baumannii by reducing the growth of bacterial biofilm and decreasing the expression of abaI as a gene involved in A. baumannii biofilm formation.

Keywords: Acinetobacter baumannii; Antimicrobial photodynamic therapy; Antimicrobial sonodynamic therapy; Biofilms; Drug resistance; Nosocomial infection.

Fig. 1

Characterization of synthesized hypericin nanoparticle (HypNP): a) Transmission electron microscope (TEM) image (Scale bar = 200 nm), b) The size distribution profile of HypNP

Fig. 2

Effects of different treatment groups on the cell viability of Acinetobacter baumannii. *Significantly different from the control group (no treatment), P < 0.05

Fig. 3

Effects of different treatment groups on the biofilm of Acinetobacter baumannii. *Significantly different from the control group (no treatment), P < 0.05

Fig. 4

Confirmation of quality of AbaI structure by a. The three-dimensional modeling of 3P2F; b. The Ramachandran plot of 3P2F; c. Verify_3D; and d. ERRAT

Fig. 5

Protein-protein interactions network analysis of AbaI

Fig. 6

Representation of docked ligand-protein complex; Interaction of Hypericin with amino acid residues of AbaI

Fig. 7

Effects of different treatment groups on the expression of gene involved in biofilm formation of Acinetobacter baumannii. *Significantly different from the control group (no treatment), P < 0.05