Antimicrobial Silver

Antibiotic-resistant bacteria are an increasing problem. Silver nanoparticles (AgNPs) have bactericidal activity against a broad spectrum of bacteria, including highly resistant strains, and are efficient at low concentrations. AgNPs are thought to work synergistically with antibiotics to kill bacteria through a mechanism that is not entirely understood.

The purpose of this study was to evaluate synergistic effects of antibiotics administered at doses lower than their minimum inhibitory concentration (MIC) with AgNPs of 2 sizes (28 nm and 8 nm). Effects were quantified and classified as synergistic, additive, indifferent, or antagonistic. Gram-positive bacterial growth was inhibited less by AgNPs than gram-negative bacterial growth, and the antibacterial activity of smaller AgNPs was stronger than for larger AgNPs. The most common synergistic effects were observed when AgNPs were combined with gentamicin. The highest enhancement of antibacterial activity was seen when penicillin G was combined with AgNP to treat Actinobacillus pleuropneumoniae. The authors conclude that AgNPs have potential as adjuvants for treating veterinary bacterial diseases and reducing antibiotic use.

With the rising incidence of multiantibiotic-resistant bacteria in human and veterinary medicine, this article is highly relevant to modern wound care. Silver—shown to have broad-spectrum antimicrobial activity—has been used to treat burn wounds for centuries. The challenge of using silver compounds is maintaining an effective bactericidal silver concentration in the wound bed without causing tissue toxicity or impaired healing.¹ The results of this study are encouraging. It is unclear, however, whether the formulation, concentration, and system of silver delivery is useful for and compatible with wound healing. This would be critical information in determining the clinical relevance of findings and planning the next phase of research.—Sara Colopy, DVM, DACVS, University of Wisconsin