Antibacterial Effects of Nanobubble Water and Its Potential Application in Healthcare-associated Infection Control

Healthcare-associated infections (HAIs) remain a major cause of morbidity in hospitalized patients and residents of long-term care facilities. Conventional chemical disinfectants have limitations such as corrosion, toxicity, and economic burden. This study investigated the antibacterial properties of nanobubble water (NBW) as a novel physicochemical disinfection method that does not require chemical additives.

NBW was generated using four gases-air, nitrogen (N₂), oxygen (O₂), and carbon dioxide (CO₂)- and tested against Escherichia coli (E. coli), Extended-spectrum beta-lactamase (ESBL)-producing E. coli, Staphylococcus aureus, and Methicillin-resistant S. aureus (MRSA). Nanobubble size and stability were analyzed, and time-dependent antibacterial activity was evaluated by colony-forming unit (CFU) assays. Transmission electron microscopy (TEM) was used to assess bacterial ultrastructural changes following NBW exposure.

Generated nanobubbles measured 50-100 nm in diameter and were stable over time. NBW exhibited intrinsic, time-dependent antibacterial effects that were independent of the solvent or dissolved gas itself. Antibacterial activity was more pronounced at lower bacterial loads and differed by gas type and bacterial species: N₂-NBW was particularly effective against MRSA, whereas CO₂-NBW and Air-NBW showed activity against ESBL-producing E. coli. Several NBW types demonstrated antibacterial effects against drug-resistant strains, although the magnitude and duration varied. Importantly, short-term exposure (≤60 min) did not reduce bacterial counts, indicating that measurable effects require prolonged immersion.

NBW generated using relatively safe and inexpensive gases (excluding ozone, which is known to be cytotoxic) exerts reproducible antibacterial activity against diverse bacterial species, including resistant strains. However, its lack of rapid disinfectant action suggests that NBW is better suited for long-term immersion rather than short-contact disinfection. These findings support NBW as a potential safer and cost-effective strategy for immersion-based infection control and mitigation of antimicrobial resistance.