Antiviral activity of mycosynthesized silver nanoparticles against herpes simplex virus and human parainfluenza virus type 3

Abstract

The interaction between silver nanoparticles and viruses is attracting great interest due to the potential antiviral activity of these particles, and is the subject of much research effort in the treatment of infectious diseases. In this work, we demonstrate that silver nanoparticles undergo a size-dependent interaction with herpes simplex virus types 1 and 2 and with human parainfluenza virus type 3. We show that production of silver nanoparticles from different fungi is feasible, and their antiviral activity is dependent on the production system used. Silver nanoparticles are capable of reducing viral infectivity, probably by blocking interaction of the virus with the cell, which might depend on the size and zeta potential of the silver nanoparticles. Smaller-sized nanoparticles were able to inhibit the infectivity of the viruses analyzed.

Keywords: antiviral; herpes simplex virus; parainfluenza virus; silver nanoparticles.

Figure 1

(A) Morphology of fungi observed by optical microscopy. growth of Alternaria species (a) colony on potato dextrose agar, (b) conidia; Fusarium oxysporum, (c) colony on potato dextrose agar, (d) macroconidia; Curvularia species, (e) colony on potato dextrose agar, (f) conidia; Chaetomium indicum (g) colony on potato dextrose agar, (h) pycnidium and setae; Phoma species, (i) colony on potato dextrose agar, and (j) pycnidia of Phoma species. (B) Ultraviolet-visible spectra of five fungal cell filtrates (control, inset A). (A_C), (B_C), (C_C), (D_C), (E_C) and silver nanoparticles (experimental, inset B). (A_E), (B_E), (C_E), (D_E), and (E_E) for Alternaria species, F. oxysporum, Curvularia species, C. indicum and Phoma species, respectively.

Figure 2

Nanoparticle tracking analysis (Nanosight-lM 20; Nanosight ltd., amesbury, UK) to detect the number and size of the nanoparticles in real time. The histogram shows the nanoparticle size distribution (A) Alternaria species, 46 nm, (B) Fusarium oxysporum, 20 nm, (C) Curvularia species, 30 nm, (D) Chaetomium indicum, 50 nm, and (E) Phoma species, 40 nm. Abbreviation: con/ml E6, concentration/ml × 10⁶.

Figure 3

Transmission electron micrographs showing spherical and polydispersed silver nanoparticles. (A) Alternaria species, (B) Fusarium oxysporum, (C) Curvularia species, (D) Chaetomium indicum, and (E) Phoma species (scale 100 nm). The diameters of the nanoparticles cover a range of 4–31 nm.

Figure 4

Cotreatment assay. Vero monolayers infected with HSV-1 (A), HSV-2 (B), or HPIV-3 (C) were treated with increasing concentrations of silver nanoparticles, then overlain with carboxymethyl cellulose and incubated for 48 hours (HSV-1 and HSV-2) or 72 hours (HPIV-3) at 37°c. Plaque numbers were scored and percent inhibition was calculated with respect to “no-compound” control experiments. The data shown represent the average values for each experiment performed in triplicate. Abbreviations: HSV-1, herpes simplex virus type 1; HSV-2, herpes simplex virus type 2; HPIV-3, human parainfluenza virus type 3; sp, species.

Figure 5

Pretreatment assay. Vero monolayers were treated with increasing concentrations of silver nanoparticles and then infected with HSV-1 (A), HSV-2 (B), or HPIV-3 (C), then overlain with carboxymethyl cellulose and incubated for 48 hours (HSV-1 and HSV-2) or 72 hours (HPIV-3) at 37°c. Plaque numbers were scored and percent inhibition was calculated with respect to “no-compound” control experiments. The data shown represent the average values for each experiment performed in triplicate. Abbreviations: HSV-1, herpes simplex virus type 1; HSV-2, herpes simplex virus type 2; HPIV-3, human parainfluenza virus type 3; sp, species.

Figure 6

Post-treatment assay. Vero monolayers were infected with HSV-1 (A), HSV-2 (B), or HPIV-3 (C), treated with increasing concentrations of silver nanoparticles, overlain with carboxymethyl cellulose, and incubated for 48 hours (HSV-1 and HSV-2) or 72 hours (HPIV-3) at 37°c. Plaque numbers were scored and percent inhibition was calculated with respect to “no-compound” control experiments. The data shown represent the average values for each experiment performed in triplicate. Abbreviations: HSV-1, herpes simplex virus type 1; HSV-2, herpes simplex virus type 2; HPIV-3, human parainfluenza virus type 3; sp, species.

Figure 7

Virus pretreatment assay. Viral aliquots of HSV-1 (A), HSV-2 (B), and HPIV-3 (C) were incubated in the presence of different concentrations of silver nanoparticles for 2 hours at 37°c and then titrated on cell monolayers. Plaque numbers were scored and percent inhibition was calculated with respect to “no-compound” control experiments. The data shown represent the average values for each experiment performed in triplicate. Abbreviations: HSV-1, herpes simplex virus type 1; HSV-2, herpes simplex virus type 2; HPIV-3, human parainfluenza virus type 3; sp, species.