Boosting Antimicrobial Activity of Imipenem in Combination with Silver Nanoparticles towards S. fonticola and Pantoea sp.

Abstract

Silver nanoparticles have been considered as powerful antimicrobial agents recently, especially with the increasing incidence of diseases associated with biofilm and multi-drug resistant pathogens. The aim of this study was to synthesize silver nanoparticles by biological and chemical methods and combination with imipenem to eradicate biofilm-forming bacteria at phenotypic and genotypic levels. The biosynthesis of silver nanoparticles was done by using Enterobacter cloacae (cell-free suspension) while chemosynthesis was conducted using sodium borohydride. Biological and chemical silver nanoparticles were characterized by ultraviolet-visible spectrophotometry which showed absorbance peak at 400 and 390nm respectively. Fourier transformer infrared analysis revealed that carboxylic and polyphenolic groups were coated on surface of both silver nanoparticles. Scanning electron microscope and size analyser showed that the sizes of biologically and chemically silver nanoparticles were 63 nm and 25 nm, respectively. In addition, it showed the formation of cubical nanoparticles. The antimicrobial effect of synthesized silver nanoparticles were evaluated by agar well diffusion and macrodilution method to determine minimum inhibitory concentration value. The results showed that biological silver nanoparticles were more effective on biofilm forming bacteria (Serratia fonticola and Pantoea sp.) than chemical synthesized ones. In addition, the combination effect between silver nanoparticles and imipenem displayed synergistic effect. Gene expression of biofilm encoding genes (smaI and esaL) were evaluated by realtime quantitative polymerase chain reaction (RTqPCR) before and after treatment with silver nanoparticles in both types and imipenem and in combination between them. The results revealed that biological silver nanoparticles alone or in combination with antibiotics were more effective on biofilm gene expression by down regulation than other treatments.