This Article Full Text (PDF) Other Versions of this Article: AEM.02764-06v1 73/10/3239    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Niemira, B. A. Search for Related Content PubMed PubMed Citation Articles by Niemira, B. A. Agricola Articles by Niemira, B. A.

 Previous Article  |  Next Article 

Appl. Environ. Microbiol. doi:10.1128/AEM.02764-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Irradiation Sensitivity of Planktonic and Biofilm-Associated Escherichia coli O157:H7 Isolates is Influenced by Culture Conditions

Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, Wyndmoor, PA, 19038

^* To whom correspondence should be addressed. Email: Brendan.Niemira{at}ars.usda.gov.

	Abstract

Ionizing radiation effectively inactivates Escherichia coli O157:H7, but the efficacy of the process against biofilm cells vs. free-living planktonic cells is not well documented. The radiation sensitivity of planktonic or biofilm cells was determined for three isolates of E. coli O157:H7 (C9490, ATCC 35150, ATCC 43894). Biofilms were formed on sterile glass slides incubated at 37°C for either 24h, 48h or 72h. The biofilm and planktonic cultures were gamma irradiated to doses ranging from 0.0 (control) to 1.5kGy. The D₁₀ value (the dose of radiation required to reduce population by 90%) was calculated for each isolate/culture/maturity based on viable populations at each radiation dose. For each of the times sampled, the D₁₀ values of isolate 43894 planktonic cells (0.454-0.479 kGy) were significantly (P<0.05) higher than those observed for biofilm cells (0.381-0.385 kGy), indicating a significantly increased sensitivity to irradiation for cells in the biofilm habitat. At the 24h sampling time, isolate C9490 showed a similar pattern, with D₁₀ values of planktonic cells (0.653kGy) significantly higher than for biofilm cells (0.479kGy), while isolate 35150 showed the reverse, with D₁₀ values of planktonic cells (0.396kGy) significantly lower than for biofilm cells (0.526kGy). At the 48h and 72h sampling times, there was no difference in radiation sensitivity based on biofilm habitat for C9490 or 35150. Biofilm-associated cells therefore show a response to irradiation which can differ from that of planktonic counterparts, depending on isolate and culture maturity. Culture maturity was a more significant influence on irradiation efficacy of planktonic cells, but not for biofilm-associated cells of E. coli O157:H7.