The investigation for eradication and inhibition of Gram-positive and Gram-negative bacteria by metal zinc oxide nanoparticles

The purpose of the current research was to assess ZnO nanoparticles (ZnO NPs) effectiveness versus the bulk one as antibacterial agent towards Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) as well as Gram-positive bacteria (Bacillus cereus and Staphylococcus aureus). ZnO NPs were prepared through the interaction between Zn (CH₃COO) 2.2H₂O and NaOH. The titration reaction was performed by the addition of ethanol for obtaining a gel-like product. Then the gel was dried. On the other hand, the antibacterial activity assay was carried out using the agar well diffusion method. Overnight cultures of the test organisms (100 µl) were spread on tryptone soya agar in plates. Wells with diameters of about 6 mm were created aseptically and 20 µl of normal ZnO or ZnO NPs (whether Lab made or produced by Sigma) was performed at 25 or 50 μg/ml in wells against both tested Gram-negative and Gram-positive bacteria. The plates were incubated at 37 °C ± 1 °C for 24 and 48 h. Any resulting clear zone in mm (zone of inhibition) around the wells was measured. Antibacterial activity was recorded if the zone of inhibition was greater than 8 mm. The results showed that both transmission and scanning electron microscopies confirmed the nanoparticles being formed in Nano scale particles. The particle size ranged between 38.45 and 39.95 nm, with an average size 38.93 or ranged between 83.14 and 88.21 nm, with an average size 87.24 nm for Sigma or Lab made ZnO NPs, respectively. The particle size of normal was ranged between 551.25 and 553.20 nm, with an average size 552.2 nm. Z-potential for ZnO NPs showed negatively charged (-11.7 mV for Lab made and -11,6 for Sigma, respectively),while normal ZnO possessed ζ-potential value of +23.0 mV. Highest inhibition zone was observed at the concentration of 50 μg/ml ZnO NPs against all pathogens compared to lower one (25 μg/ml) of the ZnO NPs. Gram-negative bacteria, namely Escherichia coli or Pseudomonas aeruginosa exhibited relatively lower sensitivity towards ZnO, whether in the normal or rather in the NPs form (Sigma or Lab made), compared to the two studied Gram-positive bacterial strains (Bacillus cereus or Staphylococcus aureus). It could be concluded that besides ZnO, especially in the NPs form, there is a promising inorganic substance with numerous applicable benefits in a wide range of industries. It is has a harmful impact against considerable pathogenic strains.