Photodynamic antibacterial enhanced effect of methylene blue-gold nanoparticles conjugate on Staphylococcal aureus isolated from impetigo lesions in vitro study

• Methylene blue gold nanoparticles conjugate effect was evaluated on S. aureus.
• The photoactivated MB-gold nanoparticles showed the maximum inhibitory effect.
• No inhibitory effect of MB-gold nanoparticles was observed without laser use.
• Diode laser enhanced a significant inhibitory effect of gold nanoparticles.
• Methylene blue showed no significant inhibitory effect on S. aureus.

SummaryBackgroundStaphylococcal aureus is the most common organism which has been encountered in impetigo infection. Gold nanoparticles can be used as a tool to deliver antimicrobials or to enhance photodynamic destruction of bacteria.ObjectiveTo evaluate the photodynamic effect of methylene blue gold nanoparticles (MB-gold nanoparticles conjugate) on S. aureus which were isolated from impetigo lesions.Patient and methodsTwenty children were diagnosed clinically as impetigo, and aged from 3 to 5 years of both sexes were recruited in the study. Two bacteriological samples were collected from each patient, identified and cultured. Samples of S. aureus of a concentration of 10−1 ml were divided into four groups. S. aureus was treated by MB-gold nanoparticles conjugate, gold nanoparticles, MB, and the fourth group served as a control group. Diode laser (660 nm) was used for photoactivation. The bacterial growth inhibition was determined by two methods: the percentage of reduction of viable bacteria count and the optical density (O.D) of bacterial growth.ResultsThe highest significant inhibitory effect on S. aureus was obtained with MB-gold nanoparticles conjugate when irradiated by diode laser 660 nm (P < 0.0001). The percentage of viable bacteria was 3%. The photoactivated gold nanoparticles showed a significant inhibitory effect on bacterial growth (P < 0.05). A non-significant inhibitory effect was elicited in other groups.ConclusionThe photoactivated MB-gold nanoparticles conjugate showed the maximum inhibitory effect on S. aureus activity. The gold nanoparticles proved efficacy as a drug delivery system. It enhanced the photodynamic antibacterial effect of methylene blue.