Enhanced Decontamination ofBacillusSpores in a Simulated Drinking Water System by Germinant Addition

Abstract

Contact with germinant solutions followed by commonly used disinfectants as a means to decontaminate Bacillus spores in a model drinking water system was investigated. Biofilms composed of indigenous water system bacteria were accumulated on materials commonly used for residential plumbing, polyvinyl chloride (PVC), and copper, in a continuously stirred tank reactor for controlled shear. Once the biofilms were established, Bacillus thuringiensis kurstaki or B. anthracis Sterne spores were added to the reactor. Pipe surfaces were studied for biofilm accumulation, spore adhesion, and disinfectant (chlorine and monochloramine) susceptibility before and after germinant (1 mM inosine and 8 mM L-alanine) addition. High disinfectant concentrations (up to 100 mg/L free chlorine and 10 mg/L monochloramine) yielded less than a 2 log10 reduction in biofilm-associated viable spores after 60 min. A 4 log10 reduction in the associated spores was observed when coupons were contacted with germinants (24 h) prior to sampling. Germinant contact followed by heat (50°C, 25 min) or disinfection resulted in a greater than 4 log10 reduction in the associated viable spores. Contact with germinants resulted in dramatically enhanced susceptibility of surface-associated spores to elevated water temperature and disinfectants.