Biological synthesis of copper nanoparticles and its antimicrobial potential on selected bacteria food-borne pathogens

Abstract

In this study, copper nanoparticle (CuNPs) was synthesized using green technology and the CuNPs was characterized with Energy Dispersive X-ray (EDX) which confirmed the presence of copper. Scanning Electron Microscopy (SEM) showed the morphology and the average size was calculated to be 2.47 ± 1 nm. The functional groups were identified by Fourier transform infrared spectroscopy (FTIR) and this revealed that OH functional group was anchored on the surface of the nanoparticles. Antimicrobial activity of the synthesized
CuNPs was investigated at varying concentrations (0.25, 0.5, 1, 2, 3, 4, 5, 6 and 7 mg/ml) dissolved in 100% dimethyl sulfoxide (DMSO). It was tested against five food borne pathogenic organisms: Salmonella typhimurium, Methicillin resistant Staphylococcus aureus  (MRSA), Enterococcus faecalis, Shigella flexneri, and Acinetobacter baumannii using the Kirby Bauer disc diffusion and agar well   method. The results showed that the antimicrobial zone of inhibition increased with an increase in concentration of the CuNPs, an  average diameter of 25 mm at 7 mg/ml, 22 mm at 5 mg/ml and an average diameter of 13 mm at 2 mg/ml of 100% DMSO.  Nanoparticles at 0.25 mg/ml and 0.5 mg/ml concentration failed to produce any clear zone across all the test organisms while only Enterococcus faecalis was sensitive with a clear zone diameter of 10 mm at 1 mg/ml CuNPs. MRSA has the least susceptibility: 9 mm clear zone diameter at 2 mg/ml and at 7 mg/ml clear zone diameter of 20 mm, relative to other tested organisms. The test organisms were not sensitive to the following conventional antibiotics: Cefuroxime, Ceftazidime, Erythromycin, Amoxicillin/Clavulanic acid and Cloxacillin, but only sensitive to Gentamicin, Ceftriaxone and Ofloxacin. MRSA on the other hand was not sensitive to all the eight antibiotics tested but susceptible to the CuNPs. The results obtained from this study indicated that copper nanoparticles can be used in the food industry to control both Gram positive and negative bacteria tested.

Keywords: Synthesis, Copper nanoparticles, Antimicrobial activities, Bacteria.