Antibacterial effect of gold nanoparticles against Corynebacterium pseudotuberculosis

Corynebacterium pseudotuberculosis is the etiological agent of chronic caseous lymphadenitis. The bacterium infects goats and sheep causing great economic loss worldwide annually. The present work aims to evaluate the efficiency of gold nanoparticles (AuNPs) and AuNPs - laser combined therapy as antibacterial approaches against C. pseudotuberculosis bacteria in vitro. Gold nanoparticles 25 nm were synthesized by co-precipitation method and characterized by different techniques including; Transmission Electron Microscope (TEM), X-ray Diffraction and Dynamic Light Scattering. Three concentrations of AuNPs (50, 100 and 200 μg/mL) were utilized for estimating the bacterial growth rate and the Minimum Inhibitory Concentration (MIC). The mechanism of interaction between AuNPs and bacteria was evaluated by transmission electron microscopic image analysis. Confocal Laser Scanning Microscopic technique was used to study the cytotoxic action of AuNPs and laser against C. psudotuberculosis. Results revealed that MIC of AuNPs and AuNPs - laser combined therapy were 200 μg/mL and 100 μg/mL respectively. TEM image analysis illustrated that gold nanoparticles penetrated the thick wall of C. psudotuberculosis and accumulated as intracellular agglomerates. Laser light enhanced the antimicrobial activity of gold nanoparticles by at least one fold due to its photo thermal combined effect that might be used as an effective antibacterial approach against C. pseudotuberculosis.