Synthesis of compounds that can prevent bacterial resistance is of huge interest and gaining immense popularity. Cobalt (Co) is one of the cheaper transition metals and its nano form has not been studied in details for antibacterial actions. Comparative analysis of Co nanoparticles with bulk Co and standard antibacterials are also lacking. In our study, concentration dependent action of Co nanoparticles was observed from 0.125 to 128.0 µg/ml against S. aureus and E. coli. Zone of inhibition of Co nanoparticles was better against E. coli than S. aureus. Co nanoparticles were markedly betterthan bulk Co, oxytetracycline and gentamicin. Activity index and fold increase of Co nanoparticles were higher at most of the concentrations. In conclusion, Co nanoparticles showed better antibacterial action than other tested compounds against S. aureus and E. coli particularly at lower concentrations, and their use may be extended in different biomedical fields in future.

Bacterial resistance to antibiotic treatment is a major emerging clinical and public health issue across the globe. Advancements in the field of metal oxide nanomaterials in the last few years have improved the potential of metal oxides in different applications. Metal oxides, of which, nickel oxide (NiO) is one, also possess antibacterial activities. This investigation was planned to synthesize NiO nanoparticles to study their antibacterial potential in comparison with bulk NiO and standard antibiotics at different concentrations. Synthesis and characterization of NiO nanoparticles was done by standard procedures. The antibacterial potentials of different compounds were determined at different concentrations against S. aureus and E. coli. The diameter of zone of inhibition showed that the antibacterial effect of NiO nanoparticles against S. aureus was better than E. coli at the same concentration. The concentration-dependent effect of NiO nanoparticles was observed from 0.125 to 128 µg/ml. The effect of NiO nanoparticles was markedly better than bulk NiO at all concentrations. Tetracycline and gentamicin did not show effect below 1.0 µg/ml and 2.0 µg/ml, respectively. The activity index and fold increase of NiO nanoparticles were both higher than 1 and positive, with respect to tetracycline, gentamicin and bulk NiO against S. aureus and E. coli at all the tested concentrations. In conclusion, the NiO nanoparticles seemed to be a more potent antibacterial agent than their bulk form, tetracycline and gentamicin, and in future, their applications may be extended in biomedical field and other areas to reduce microbial infections and incidences of antibacterial resistance.

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The promising results of metal oxides nanoparticles in different areas including the biological system lead us to investigate the antioxidant and antimicrobial actions of chemically synthesized cobalt oxide (Co3O4) nanoparticles. The different concentrations of synthesized Co3O4 nanoparticles were prepared and evaluated for different parameters at different time intervals i.e.  on day 1, 30 and 60 after preparations.  Co3O4 nanoparticles synthesized in this study were of 52.2 nm average size with a polydispersity index of 0.465. We observed that Co3O4 nanoparticles scavenge different in vitro free radicals (DPPH, ABTS, superoxide anion and hydrogen peroxide radicals) in concentration dependent manner. The percentage of inhibitions of free radicals by Co3O4 nanoparticles was markedly more on day 1 as compared to day 30 and 60. The IC50 values of Co3O4 nanoparticles for these free radicals were also on day 1 as compared to day 30 and 60. The Co3O4 nanoparticles showed the antibacterial actions against both the bacterial strains i.e. S. aureus and E. coli. The MIC and MBC values revealed that action of Co3O4 nanoparticles was more against E. coli than S. aureus. The MIC and MBC values were lower on day 1 as compared to day 30 and 60 with respective to specific bacteria. In conclusions, the Co3O4 nanoparticles synthesized in this study showed potent antioxidant and antibacterial properties due to which it may serve as promising candidate for the combat the biological problems humans, animals and plants associated with reactive oxygen species and bacteria.