• Synergistic Effect of Silver Nanoparticles with Cephalexin and penicillinV Antibiotics on Mastitis-causing Staphylococcus aureus
  • Atena Bazjoo,1,*
    1. Department of Microbiology, Science Faculty, Islamic Azad University of Arak, Iran


  • Introduction: mastitis is one of the most costly disease in dairy cows, which greatly decreases milk production. Use of antibiotics in cattle leads to antibiotic-resistance of mastitis-causing bacteria. The present study aimed to investigate synergistic effect of silver nanoparticles (AgNPs) with Kanamycin or gentamicin antibiotic on mastitis-causing Staphylococcus aureus.
  • Methods: In this study, 150 samples of milk were taken from the cows with clinical and subclinical mastitis during the august-October 2017 sampling period. In addition to biochemical tests, nuc gene amplification by PCR was used to identify strains of Staphylococcus aureus. Disk diffusion test and microdilution were performed to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Fractional Inhibitory Concentration (FIC) index was calculated to determine the interaction between a combination of AgNPs and each one of the antibiotics
  • Results: Twenty strains of Staphylococcus aureus were isolated from 150 milk samples and were confirmed by PCR. Based on disk diffusion test, 25%, 20% and 55% of the strains were respectively susceptible, moderately susceptible and resistant to gentamicin. In addition, 35%, 15% and 50% of the strains were respectively susceptible, moderately susceptible and resistant toKanamycin. According to FIC index, gentamicin antibiotic and AgNPs had synergistic effects in 50% of the strains. Furthermore, Kanamycin antibiotic and AgNPs had synergistic effects in 45% of the strains.
  • Conclusion: It can be concluded that a combination of AgNPs with either gentamicin or Kanamycin showed synergistic antibacterial properties in Staphylococcus aureus isolates from mastitis. In addition, some hypotheses were proposed to explain antimicrobial mechanism of the combination
  • Keywords: Staphylococcus aureus, mastitis, silver nanoparticles, gentamicin, Kanamycin , synergistic