Effect of Electrolyzed Water on the Disinfection of Bacillus cereus Biofilms: The Mechanism of Enhanced Resistance of Sessile Cells in the Biofilm Matrix

This study examined the disinfection efficacy and mechanism of electrolyzed water (EW) on Bacillus cereus biofilms. B. cereus strains, ATCC 14579 and Korean Collection for Type Cultures (KCTC) 13153 biofilms, were formed on stainless steel (SS) and plastic slide (PS) coupons. Mature biofilms were treated with slightly acidic EW (SAEW), acidic EW (AEW), and basic EW (BEW). SAEW (available chlorine concentration, 25 ± 1.31 mg L^-1; pH 5.71 ± 0.16; and oxidation reduction potential, 818 to 855 mV) reduced ATCC 14579 biofilms on plastic slides to below the detection limit within 30 s. However, biofilms on SS coupons showed a higher resistance to the SAEW treatment. When the disinfection activities of three types of EW on biofilms were compared, AEW showed a higher bactericidal activity, followed by SAEW and BEW. In contrast, BEW showed a significantly ( P < 0.05) higher biofilm dispersal activity than AEW and SAEW. SAEW disinfection of the B. cereus biofilms was due to the disruption of the B. cereus plasma membrane. The higher resistance of biofilms formed on the SS coupon might be due to the higher number of attached cells and extracellular polymeric substances formation that reacts with the active chlorine ions, such as hypochlorous acid and hypochlorite ion of SAEW, which decreased the disinfection efficacy of SAEW. This study showed that the EW treatment effectively disinfected B. cereus biofilms, providing insight into the potential use of EW in the food processing industry to control the biofilm formation of B. cereus.

The Efficacy of an Electrolysed Water Formulation on Biofilms

Electrolysed water is a basic process whereby an electric current is passed through deionised water containing a low concentration of sodium chloride in an electrolysis chamber, which results in a more complex chemistry resulting in the production of a strong bactericidal and fungicidal solution at the anode. This microbicidal solution contains hypochlorous acid that is fast-acting and environmentally safe, as upon bacterial killing, the equilibrium shifts from hypochlorous acid back to salt and water. Other antimicrobial agents produced in this process include sodium hypochlorite and chlorine. The use of electrolysed water formulations in wound care to control wound bioburden is underway. However, there is limited evidence of the efficacy of electrolysed water on the control of biofilms, which are renowned for their tolerance to a variety of antimicrobials. Therefore this study aimed to assess a new electrolysed water formulation on in vitro Staphylococcus aureus and Pseudomonas aeruginosa biofilms. Results showed that the electrolysed water formulation effectively reduced biofilm in all models following a 15 min contact time. Microbial cell counts confirmed the reduction biofilm bacteria. Additional cytotoxicity using L929 fibroblasts confirmed that a 50% and 25% dilution of the electrolysed water formulation was non-cytotoxic to cells. In conclusion, this study has confirmed that the application of a new electrolysed water product effectively removed biofilm after a short exposure time. The use of this technology as a wound cleanser may help to control existing biofilms in complicated, non-healing wounds.