Antimicrobial potency of colloidal silver compared with antibiotic eye drops

Abstract

Objectives: This study determined the antimicrobial potency of colloidal silver against Escherichia coli, Staphylococcus epidermidis, Staphylococcus aureus, and Bacillus subtilis compared with that of tobramycin, lomefloxacin, and moxifloxacin eye drops.

Methods: Three concentrations of colloidal silver (10, 20, and 30 ppm) were impregnated in filter paper discs placed on the surface of agar inoculated with test organisms, namely, Escherichia coli, Staphylococcus epidermidis, Staphylococcus aureus, and Bacillus subtilis. Antibacterial-activity testing (ABAT) and Kirby Bauer disc diffusion were employed to test the antimicrobial potency of colloidal silver against ophthalmic antibiotics (tobramycin, lomefloxacin, and moxifloxacin). Resulting zones of inhibition of the antimicrobials tested were compared with those of the control antibiotic ampicillin. Sensitivity and resistance of the different pathogens were determined.

Results: Twenty-two-millimeter zones of inhibition in the Kirby Bauer were observed in the 30 ppm preparation of colloidal silver for both S. aureus and B. subtilis, showing strong inhibitory activity compared with ampicillin (16 mm and 10 mm respectively). A 12-mm zone of inhibition was measured for S. epidermidis, showing slight inhibitory activity. ABAT showed that E. coli, S. epidermidis, S. aureus, and B. subtilis were resistant to the different concentrations of colloidal silver but sensitive to ampicillin, tobramycin, lomefloxacin, and moxifloxacin.

Conclusions: Kirby Bauer disc-diffusion test demonstrated that S. epidermidis, S. aureus, and B. subtilis were sensitive to the 30-ppm concentration of colloidal silver. On the other hand, ABAT yielded negative results for colloidal silver at 10, 20, 30 ppm when tested against these organisms.