Effects of bacterial concentrations and centrifugations on susceptibility of Bacillus subtilis vegetative cells and Escherichia coli O157:H7 to various electrolyzed oxidizing water treatments |
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| Affiliation: | 1. Food Assurance and Meat Science Team, Food and Bio-based Products Group, AgResearch, Ruakura Research Centre, 10 Bisley Road, Hamilton, New Zealand;2. Dairy Foods Team, Food and Bio-based Products Group, AgResearch, Ruakura Research Centre, 10 Bisley Road, Hamilton, New Zealand;3. Food Assurance and Meat Science Team, Food and Bio-based Products Group, AgResearch, Hopkirk Research Institute, Massey University, Corner University Ave and Library Road, Palmerston North, New Zealand;1. Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Vic 3010, Australia;2. Department of Agriculture and Food WA, Baron Hay Court South Perth, WA 6151, Australia;3. AgResearch Limited, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton 3240, New Zealand;4. Biosciences Research Division, Department of Primary Industries, 1 Park Drive, Bundoora, Vic 3083, Australia;5. Future Farming Research Division, Department of Primary Industries, 1 Park Drive, Bundoora, Vic 3083, Australia;6. Future Farming Research Division, Department of Primary Industries, 600 Sneydes Rd, Werribee, Vic 3030, Australia;7. Cooperative Animal Research Centre for Sheep Industry Innovation, CJ Hawkins Homestead Building, University of New England, Armidale, NSW 2351, Australia |
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| Abstract: | This study discussed the effects of different bacterial concentrations and centrifugations on the antimicrobial efficacy of electrolyzed oxidizing (EO) water on Bacillus subtilis and Escherichia coli O157:H7. Overnight grown bacterial cultures were centrifuged 1 to 3 times and bacterial concentrations were adjusted to approximately 9 (high), 7 (medium), or 5 (low) log10 CFU/mL. Antimicrobial efficacy of acidic EO water (AEW) and neutral pH EO water (NEW) containing 0.25–30 mg/L available chlorine was determined. In order to ascertain the effects of AEW and NEW on targeted pathogens, cellular properties at bio-molecular levels were also studied. The results showed that the susceptibility of both pathogens decreased significantly with increasing bacterial concentrations. AEW with 10, 0.25 and 0.25 mg/L and NEW with 30, 0.5 and 0.25 mg/L available chlorine were needed for high, medium and low bacterial concentrations, respectively to non-detectable levels by direct plating for E. coli O157:H7. B. subtilis was found more resistant to both EO water treatments and only 4.1 and 3.8 log reductions were achieved for AEW and NEW containing 30 mg/L available chlorine. On the other hand, it was observed that as centrifugation time increased, both bacteria became significantly more sensitive to EO water treatments. When centrifugation period increased from 1 to 3 times, additional 2.67 and 3.38 log E. coli O157:H7 reductions were observed for AEW and NEW treatments, respectively. A similar trend was observed for B. subtilis. DNA and protein leakage increased when pathogens were treated by AEW and NEW with increasing available chlorine concentration, but decreased DNA and protein leakage were observed with increased centrifugation times. These results indicate that initial bacterial concentration and the centrifugation time are two important factors and should be carefully considered in chlorine-based antimicrobial efficacy testing. |
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| Keywords: | EO water Initial bacterial concentration Centrifugation time |
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