TITLE:
Synergistic Effect of Silver Nanoparticles with Neomycin or Gentamicin Antibiotics on Mastitis-Causing Staphylococcus aureus
AUTHORS:
Shahab Jamaran, Bahareh Rahimian Zarif
KEYWORDS:
Staphylococcus aureus, Mastitis, Silver Nanoparticles, Gentamicin, Neomycin, Synergistic
JOURNAL NAME:
Open Journal of Ecology,
Vol.6 No.7,
June
21,
2016
ABSTRACT: Objective: Mastitis is one of the most costly
diseases 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
neomycin or gentamicin antibiotic on mastitis-causing Staphylococcus aureus. Materials and Methods: In
this study, 46 samples of milk were taken from the cows with clinical and subclinical
mastitis during the august-October 2015 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 46 milk samples and were confirmed by PCR. Based on
disk diffusion test, 35%, 10% 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
to neomycin. According to FIC index, gentamicin antibiotic and AgNPs had synergistic
effects in 50% of the strains. Furthermore, neomycin antibiotic and AgNPs had synergistic
effects in 45% of the strains. Conclusion: It could be concluded that a combination of AgNPs with either gentamicin
or neomycin showed synergistic antibacterial properties in Staphylococcus aureus isolates from mastitis. In addition, some hypotheses were proposed to explain antimicrobial
mechanism of the combination.