Silver nanoparticle treatment partially restores antibiotic activity by reducing the number of isolates with antibiotic-resistant genes in cows with mastitis

In recent years, intensive use of antibiotics has led to bacterial strains developing resistance, which decreases their effectiveness in disease treatments. One of the approaches for combating resistance is combinational therapies, which consist of the use of antibiotic resistance inhibitors in combination with antibiotics. Our group is developing a new approach, consisting of therapy with AgNPs as an inhibitor, without combination with antibiotics. The aim of this work was to study in vivo on 744 cows with serous mastitis and in relation to 31 antibiotics: (1) the capacity of cow therapy with AgNPs to modulate mecA (S. aureus), blaGES and blaDHA (E. coli) resistance genes, and (2) compare the results with those obtained for therapy with antibiotic medicine. The data obtained after AgNP therapy showed a 40.3 % and 54.5 % reduction in antibiotic-resistant S. aureus and E. coli isolate numbers, respectively, whereas they increased by 48.9 % and 114.9 % after antibiotic therapy. The percentage of isolates with detected drug-resistant genes decreased on average by 22.7 % after AgNP treatment, while they increased on average by 36.9 % after antibiotic therapy. This decrease of resistance genes in isolates caused by AgNP therapy is the fifth route of combating bacterial resistance with AgNPs, in addition to four routes revealed by our group. These findings provide further insight into the origins of the capacity of AgNP therapy to combat resistance.