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Appl. Environ. Microbiol. doi:10.1128/AEM.02899-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Persistence and decontamination of Bacillus atrophaeus subsp. globigii spores on corroded iron in a model drinking water system

Department of Civil and Environmental Engineering, 765 Baldwin Hall, University of Cincinnati, Cincinnati, OH, 45221; National Homeland Security Research Center, Water Infrastructure Protection Division, United States Environmental Protection Agency (MS 163), Cincinnati, OH, 45268

^* To whom correspondence should be addressed. Email: szabo.jeff{at}epa.gov.

	Abstract

Persistence of Bacillus atrophaeus subsp. globigii (BG) spores on corroded iron coupons in drinking water was studied using a biofilm annular reactor. Spores were inoculated at 10⁶ CFU/ml in the dechlorinated reactor bulk water. The dechlorination allowed for observation of the effect of hydraulic shear and biofilm sloughing on persistence. Approximately 50% of the spores initially adhered to the corroded iron surface were not detected after one month. Addition of a stable 10 mg/L free chlorine residual after one month led to a 2 log₁₀ reduction of adhered BG, but levels on the coupons quickly stabilized thereafter. Increasing the free chlorine concentration to 25 or 70 mg/L had no additional effect on inactivation. BG spores injected in the presence of a typical distribution system chlorine residual (0.75 mg/L) resulted in a steady reduction of adhered BG over one month, but levels on the coupons eventually stabilized. Adding elevated chlorine levels (10, 25 and 70 mg/L) after 1 month had no effect on the rate of inactivation. Decontaminating with elevated free chlorine levels immediately after spore injection resulted in 3-log₁₀ reduction within two weeks, but rate of inactivation leveled off afterward. This indicates that free chlorine did not reach portions of the corroded iron surface where BG spores were adhered. BG spores are capable of persisting for an extended time in the presence of high levels of free chlorine.

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