Surface plasmon resonance-induced photoactivation of gold nanoparticles as bactericidal agents against methicillin-resistant Staphylococcus aureus

Figures & data

Figure 1 Schematic illustration of the proposed antimicrobial nanotherapy against MRSA, using laser pre-irradiated gold nanoparticles.

Abbreviation: MRSA, methicillin-resistant Staphylococcus aureus.

Figure 2 (A) Transmission electron micrographs of the GNPs used for the experiments. The scale bar represents 100 nm. (B) Ultraviolet-visible relationship between peak wavelength and laser power in the pre-GNPs (black spectra 0.5 W/cm²; blue spectra 1 W/cm²). (C) Phase contrast microscopy of MRSA treated with GNPs alone (5 mg/L). (D) Phase contrast microscopy of MRSA treated with pre-GNPs (5 mg/L).

Abbreviations: GNP, gold nanoparticle; MRSA, methicillin-resistant Staphylococcus aureus.

Figure 3 Immunofluorescence microscopy (LIVE/DEAD® Baclight™ Bacterial Viability Kit; Life Technologies, Carlsbad, CA, USA) of the bacterial population following treatment with 5 mg/L GNPs/pre-GNPs at various incubation times (red, dead bacteria; green, live bacteria). The merged images represent the superposition of dead and live bacteria.

Abbreviation: GNP, gold nanoparticle.

Table 1 Minimum inhibitory concentration of GNPs against MRSA

Well	Percentage	GNPs	Pre-GNPs
1	100	−	−
2	50	−	−
3	25	−	−
4	12.5	+	−
5	6.25	+	−
6	3.13	+	+
7	1.56	+	+
8	0.78	+	+
9	0.39	+	+
10	0.20	+	+
11	0.10	−	−
12	−	+	+

Notes: +, growth of bacteria; −, no growth of bacteria; well 11, negative control; well 12, positive control.

Abbreviations: GNP, gold nanoparticle; MRSA, methicillin-resistant Staphylococcus aureus.

Figure 4 Flowcytometric quantification of bacterial lysis in MRSA microorganism following pre-GNPs treatment.

Notes: (A and B) representative FACS dot plots (red fluorescence[FL3] versus forward scatter[FSC]) gated on MRSA population are shown. (B) show increased red fluorescence (FL3) suggesting high viability loss after LASER irradiation following incubation for 1 hour with 5 mg/L pre-GNPs compared with GNPs only (A). (C and D) display histogram representation of red fluorescence, (dead bacteria) in LASER treated MRSA population following GNPs treatment (C) or pre-GNPs (D).

Abbreviations: FACS, fluorescence-activated cell sorting; GNPs, gold nanoparticles; MRSA, methicillin-resistant Staphylo coccus aureus.

Figure 5 Results of experimental seriate exposure of MRSA to gold nanoparticles in different concentrations.

Notes: Bars represent median dead bacteria percent as calculated by flow cytometry. Error bars represent range of dead bacteria percent. MRSA treated with GNPs only (control) for 60 seconds (A) and 30 minutes (B) at concentrations ranging from 1 mg/L to 50 mg/L resulted in significantly lower necrotic rates. Following treatment for 60 minutes (C) the percentages of MRSA necrosis among the two GNPs solutions in low concentrations (<20 mg/L) was statistically significant. Treatment with high concentration of GNPs for a long period of time (24 hours) (D) did not reveal any significance in terms of necrotic percentage among the two MRSA cultures (GNPs and pre-GNPs).

Abbreviations: GNP, gold nanoparticle; MRSA, methicillin-resistant Staphylococcus aureus.