Silver nanoparticles enhance the effectiveness of traditional antibiotics against S. aureus causing bovine mastitis within the safety limit

Increasing the antimicrobial resistance associated with S. aureus mastitis challenges the therapy of such infection and results in extensive economic losses. This study revealed an increase in the efficacy of eight different antibiotics upon their combination with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs) against MDR S. aureus mastitis strain. Significant synergism was detected in PVP-AgNPs combinations with a group of antibiotics including oxytetracycline, vancomycin, ofloxacin, cefuroxime, and ampicillin/sulbactam, but the highest synergism was reported with kanamycin, chloramphenicol, and penicillin. Furthermore, the antibacterial activity of PVP-AgNPs was tested in milk compared to PBS, demonstrating that the particles remained effective against S. aureus in milk with a twofold increase in MIC compared to PBS. At a concentration of 50 μg/kg b.wt, the PVP-AgNPs showed no signs of toxicity in albino rats upon oral exposure, whereas the intraperitoneal route produced slight toxicity signs within the safety limit. Our results suggested that a strategy of combining PVP-AgNPs with antibiotics might be a magic bullet to beat S. aureus mastitis and save the dairy industry. However, further study is required to evaluate the effect in vivo using mastitis model and expand the toxicological study to include systemic absorption from mammary gland to body organs, distribution, and elimination.