Avaliação da atividade antimicrobiana de nanopartículas de óxido de zinco, óxido de cobre e prata em bactérias Gram-positivas e Gram-negativas.

Abstract

The use of antimicrobials in packages, in particular metal oxides, can be effective in inhibiting or retarding the growth of microorganisms, thus enabling a longer expiration date of foods. The main objective of this work was to synthesize, characterize and test the antimicrobial activity of zinc oxide, copper oxide and silver nanoparticles in Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli and Salmonella typhimurium). For the synthesis of ZnO nanoparticles the precipitation and sonochemistry (ultrasound) methods were performed, for CuO, besides these methods, hydrothermal and Ag precipitation were also performed. Silver, considered a universal antimicrobial, was used as a benchmark in the studies, and therefore only the most traditional synthesis (precipitation). The characterizations performed for the nanoparticles were X-Ray Diffraction (XRD), Fourier-transform infrared Spectroscy (FTIR), Scanning Electron Microscopy with Field Emission Source (FEG) and Zeta Potential. The evaluation of the antimicrobial activity was performed through the agar diffusion test (qualitative analysis) and the bottle agitation test (quantitative analysis). The latter was performed for the bacteria that showed greater inhibition of the diffusion test, S. aureus and E. coli, and for the syntheses that obtained smaller nanoparticles, being the ultrasound for ZnO, ultrasound 2 h for CuO and precipitation for Ag. The thickness of the nanoparticles (NPs) were between 10 and 40 nm. In the diffusion test the ZnONPs showed inhibition halos for S. aureus (12 mm and 14 mm ± 0,05) and E. faecalis (5 mm ± 0,05); the CuONPs formed halos for S. aureus (6.6 to 9.6 mm ± 0.05) and slightly for E. coli (4.5 to 5.2 mm ± 0.05); for AgNPs, inhibition halos were formed in all bacteria, S. aureus (12.4 ± 0.05); E. faecalis (9.7 mm ± 0.05); E. coli (8.6 mm ± 0.05) and Salmonella (8.1 mm ± 0.05).While in the bottle shake test for S. aureus the nanoparticles obtained about 100% inhibition relative to the control at a concentration of about 200 μg / ml for CuONPs and AgNPs and at 350 μg / ml for ZnONPs. For E. coli with the highest studied concentration for all NPs, 500 μg / ml, it was possible an inhibition around 90% related to the control. The antimicrobial activity of the nanoparticles used showed greater inhibition for Gram-positive bacteria compared to Gram-negative bacteria. According to the studies performed, the nanoparticles tested (ZnO, CuO and Ag) were shown to be potential antimicrobial agents. They can be considered of great importance for the purpose of investing in processes that retard / inhibit bacterial growth, with the potential of applying antimicrobial packaging for food storage.