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Effect of Freezing on Photoreactivation of Escherichia coli and Enterococcus faecalis

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The effect of freezing on photoreactivation of two strains of Escherichia coli (ATCC strain 25922 and O157:H7 strain 961019) and two strains of Enterococcus faecalis (strain ATCC 51299, vancomycin-resistant and strain ATCC 29212, vancomycin-sensitive) following ultraviolet irradiation were examined. The level of log photoreactivation of the freezing treated test organisms (frozen at −7, −15, or −30 °C then thawed at room temperature prior to ultraviolet irradiation) was compared with that of the samples that had not been frozen. Freezing had obvious impact on the response of the test organisms to visible light following ultraviolet irradiation. Significantly lower levels of photoreactivation were observed in the freezing treated cells. The effect of freezing on the ability of the test microbes to photoreactivate seems to be strain and species dependent. Overall, the experimental results suggest that less photoreactivation could be expected if freezing is used as a treatment method prior to ultraviolet disinfection.

Keywords: E. coli; Enterococcus faecalis; O157:H7; freezing treatment; photoreactivation; ultraviolet disinfection; vancomycin resistant; wastewater; water treatment

Document Type: Research Article


Publication date: June 1, 2012

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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