Enhanced antimicrobial activity of the combination of silver nanoparticles and different β Lactam antibiotics against methicillin resistant Staphylococcus aureus isolates

Abstract

Methicillin resistant Staphylococcus aureus (MRSA) has emerged as a major problem worldwide. Strong synergistic action of antibiotics combined with silver nanoparticles (AgNPs) presents a potential solution for this problem. AgNPs was prepared by Gamma- irradiation method. Eighty staphylococcus spp. were obtained out of 45 different clinical specimens; 21(46.6 %) isolates were identified as MRSA and chosen to test their susceptibility to plain AgNPs, β-lactam antibiotics and mixed solution of AgNPs /antibiotics by disc diffusion method and broth microdilution assay for detection of minimum inhibitory concentration (MIC) as well as minimum bactericidal concentrations. All MRSA isolates were full resistant to amoxicillin, ceftazidime, cefotaxime, ceftriaxone, cefepime, while 3(14.2%) were susceptible to meropenem and imipenem with MIC ≤ 20µg/ml. Plain AgNPs showed potential anti-MRSA activity, the range of inhibition zones of AgNPs ranged from 7.5 to 12 mm. Broth microdilution assay revealed that 8(38.1%) and 5(23.8%) were inhibited at concentration of 31.25 and 7.81µg/ml of AgNPs, respectively. Disc diffusion assay showed the enhancement of activity of amoxicillin/AgNPs, imipenem/AgNPs and meropenem/AgNPs combinations, the fold increase areas ranging between 33.3 to 100, 0 to 166.6 and 0 to 166.6 respectively. Additionally, MIC of amoxicillin in amoxicillin/AgNPs mixture was decreased from more than 5120 μg/ml to reach 1.95 μg/ml in 28.5% of MRSA and 0.97 μg/mL in 19 % of MRSA isolates. The enhanced activity of antibiotics, especially amoxicillin, combined with AgNPs was very high against the resistant isolates, so utilizing combination therapy is one the proposed approaches to treat MRSA bacterial infections.