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.