In vitro antimicrobial activity of colloidal nano silver

Abstract

The antimicrobial effect of colloidal nanosilver (AgNPs) at concentrations of 20 and 30 ppm against reference Esherichia coli, Salmonella enterica, Staphylococcus aureus, Clostridium perfringens, Candida albicans strains and two clinical isolates (Pseudominas aeruginosa and Streptococcus pyogenes) was tested. The classical agar diffusion method, determination of the minimum inhibitory concentrations (MIC) and the time of antimicrobial action of AgNPs were used. In the studies performed by the agar diffusion method, a very good inhibitory effect of AgNPs 30 ppm and to a much lesser extent of AgNPs 20 ppm, was reported against all studied microorganisms. The studied Gram-negative bacteria showed higher sensitivity to both preparations compared to the Gram-positive microorganisms (P>0.05). The lowest sensitivity was reported for S. aureus and C. albicans, and the highest - for P. aeruginosa and S. pyogenes. The lowest MICs of AgNPs 20 ppm were reported for P. aeruginosa and C. perfringens. For them, the MIC50 was 1 μg/mL, and for the rest - 2 μg/mL. Again, C. perfringens showed the highest sensitivity to AgNPs 30 ppm with MIC50 0.5 μg/mL, and the lowest one was that of S. aureus with MIC50 2 μg/mL. For the Gram-positive bacteria MIC values were higher than for Gram-negative ones. AgNPs 20 ppm and AgNPs 30 ppm inactivated all bacterial strains tested at final concentrations of 103 cells/mL and 104 cells/mL within 5 min; only C. albicans persisted longer. The tested microorganisms remained viable for significantly longer time in the presence of AgNPs 20 ppm and AgNPs 30 ppm when in suspensions with a density of 106 cells/mL. These results are promising for the successful use of AgNPs for disinfection, as well as for topical therapy of infections involving these bacterial species.