Role of Biofilm Formation in the Drop of Bacterial Resistance to Antibiotics after Animal Therapy with Silver Nanoparticles

Abstract

Bacterial biofilm formation poses significant consequences in the treatment of infections, leading to increased virulence and antibiotic resistance of bacteria and evasion of immune responses. Various methods aimed at preventing biofilm formation were investigated, including the use of silver nanoparticles (AgNPs). However, the previous studies were focused on the efficacy of AgNPs in vitro. In this study, we investigated the effectiveness of AgNPs in vivo in treating 700 cows with subclinical mastitis. The results obtained with AgNP therapy were compared with results obtained with first-line antibiotic-containing drug therapy. The biofilm formation index was quantified by using the crystal violet test. The number of isolates with strong and weak biofilm formation activities was assessed. Our findings demonstrate that therapy with AgNPs resulted in a reduction in the average index of biofilm-forming activity of six bacteria by 20.4% for strong biofilms and by 16.4% for weak biofilms across six bovine mastitis-causing pathogens (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus dysgalactiae, Escherichia coli, Streptococcus agalactiae, and Streptococcus pyogenes). Conversely, treatment with antibiotic-containing drug led to a 40.4% increase in the average index of biofilm-forming activity for isolates with strong biofilms and an 8.7% increase for isolates with weak biofilms. Additionally, the number of strong biofilm isolates increased by an average of 232% after the antibiotic treatment. Therefore, our study identified the fourth reason for the recently revealed phenomenon of the decrease of bacterial resistance caused by animal therapy with AgNPs, highlighting as well the potential of AgNPs as a therapeutic intervention against biofilm-associated infections. This translational research represents a significant advancement from laboratory studies to real-world applications of AgNP therapy for the decrease of bacterial antibiotic resistance.