P1-205 Determination of the State of Escherichia coli O157:H7 Cells Treated with Electrolyzed Oxidizing (EO) Water Using Flow Cytometry

Monday, July 10, 2017
Exhibit Hall (Tampa Convention Center)
G. Kwabena Afari , University of Georgia , Griffin , GA
Yen-Con Hung , University of Georgia , Griffin , GA
Introduction:  Electrolyzed oxidizing (EO) water has been shown to be highly effective in the reduction of microorganisms on foods. Concerns, however, persist that this may not lead to complete inactivation of pathogens, but results in a proportion of cells entering the viable but non-culturable (VBNC) state, which can cause serious food safety concerns.

Purpose:  This study was conducted to determine the lethality of EO water treatments on Escherichia coli O157:H7 cells and proportions of cells that enter the VBNC state using flow cytometry and plating.

Methods:  A 5-strain cocktail of E. coli O157:H7 (approx. 6 log CFU/mL) was exposed to varying free chlorine concentrations (2.5, 5, 10 mg/L) of near neutral EO (NEO) water, acidic EO (AEO) water and NaOCl solutions for 30, 60, and 120 s. Sodium thiosulfate was added as a neutralizing solution, after treatment, and cells were recovered on plates of Sorbitol MacConkey agar supplemented with nalidixic acid and sodium pyruvate, as well as Tryptic Soy enrichment broths. For VBNC determination, 3 µL of a mixture of propidium iodide and SYTOTM9 dyes was added to 1 mL of each treated sample and subsequently analyzed in a flow cytometer. Deionized water treatments served as controls and experiments were replicated three times.

Results:  Sanitizer type had a significant effect (p<0.05) on the reductions of E. coli O157:H7 observed on plates, with AEO water treatments resulting in complete inactivation of pathogens after enrichment (> 6 log CFU/mL reduction). For NEO water, growth was, only, observed after enrichment. In the case of NaOCl, longer contact times were needed to achieve significant reductions. Up to 4% of cells remained in the live region of flow cytometric profiles of NEO water and NaOCl treated cells.

Significance:  Results suggest that although EO water treatments lead to great reductions in E. coli O157:H7 cells, some cells may enter the VBNC state.