Growth Inhibition of Gram-Positive and Gram-Negative Bacteria by Zinc Oxide Hedgehog Particles

Abstract

Purpose: Nanomaterials for antimicrobial applications have gained interest in recent years due to the increasing bacteria resistance to conventional antibiotics. Wound sterilization, water treatment and surface decontamination all avail from multifunctional materials that also possess excellent antibacterial properties, eg zinc oxide (ZnO). Here, we assess and compare the effects of synthesized hedgehog-like ZnO structures and commercial ZnO particles with and without mixing on the inactivation of bacteria on surfaces and in liquid environments. Methods: Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria in microbial culture medium were added to reverse spin bioreactors that contained different concentrations of each ZnO type to enable dynamic mixing of the bacteria-ZnO suspensions. Optical density of the bacteria-ZnO suspensions was measured in real-time and the number of viable bacteria after 24 h exposure was determined using standard microbiological techniques. The concentration of zinc ion generated from ZnO dissolution in different liquid types was estimated from the dynamic interaction exposure. Static antibacterial tests without agitation in liquid media and on agar surface were performed for comparison. Results: A correlation between increasing ZnO particle concentration and reduction in viable bacteria was not monotonous. The lowest concentration tested (10 µg/mL) even stimulated bacteria growth. The hedgehog ZnO was significantly more antibacterial than commercial ZnO particles at higher concentrations (up to 1000 µg/mL tested), more against E. coli than S. aureus. Minimum inhibitory concentration in microwell plates was correlated with those results. No inhibition was detected for any ZnO type deposited on agar surface. Zinc ion release was greatly suppressed in cultivation media. Scanning electron microscopy images revealed that ZnO needles can pierce membrane of bacteria whereas the commercial ZnO nanoparticles rather agglomerate on the cell surface. Conclusion:The inhibition effects are thus mainly controlled by the interaction dynamics between bacteria and ZnO, where mixing greatly enhances antibacterial efficacy of all ZnO particles. The efficacy is modulated also by ZnO particle shapes, where hedgehog ZnO has superior effect, in particular at lower concentrations. However, at too low concentrations, ZnO can stimulate bacteria growth and must be thus used with caution.

Zinc Oxide Nanoparticles Prime a Protective Immune Response in Galleria mellonella to Defend Against Candida albicans

“…Besides, we noticed distinct aggregation of hemocytes and enhanced phagocytosis in response to ZnO-NP injection. These results were in agreement with previous research conducted in vitro that nano-ZnO films could promote microbial clearance by macrophages and polymorphonuclear leukocytes by facilitating phagocytic efficacy (Rutherford et al, 2021). It has been recently revealed that the phenoloxidase activity of G. mellonella was induced after C. albicans infection (Sheehan and Kavanagh, 2018).…”

A Comprehensive Evaluation of Mechanical, Thermal, and Antibacterial Properties of PLA/ZnO Nanoflower Biocomposite Filaments for 3D Printing Application

“…In contrast, Gram-negative bacteria have a thin, single-layered peptidoglycan, containing high lipopolysaccharides and an absence of teichoic acid. All these different cell surface compositions result in explicit differences in the sensitivity of bacteria to ZnO nanoflowers [ 42 , 43 , 44 ].…”

“…These findings are in good agreement with the reported studies [ 45 , 46 , 47 ]. It is well known that the antibacterial activity of ZnO nanoflowers is dependent on their contents, and that a higher content of ZnO nanoflowers shows higher bactericidal activity owing to their higher surface-to-volume ratios for reacting with bacterium cells [ 42 , 48 , 49 ].…”

Antibacterial and Cellular Behaviors of Novel Zinc-Doped Hydroxyapatite/Graphene Nanocomposite for Bone Tissue Engineering

“…However, as shown in the antibacterial test results presented in Figures 6 and 7, it has been found that Gram-positive bacteria are less sensitive to ZnHA nanoparticles than Gram-negative bacteria. The reason for this can be attributed to the greater thickness of the peptidoglycan layer in Gram-positive bacteria [67,68] in such a way that the predominant mechanism of inhibiting Gram-positive S. aureus bacteria by ZnHA nanoparticles can be attributed to the induction of downregulating of amino acid synthesis and dysfunction of vital bacterial enzymes [69]. Another mechanism of bacterial inhibition is related to Zn 2+ ions released from the ZnHA-rGO nanosystem into bacteria.…”