Disinfection of Bacillus anthracis Spores in Water Systems

J. B. Morrow, J. L. Almeida, L. Fitzgerald, K. D. Cole*

* signifies NIST mentor

National Institute of Standards and Technology,CSTL, Biochemical Science Division, 100 Bureau Drive MS 8312, Gaithersburg, MD  20899-8310,

jmorrow@nist.gov Bldg. 227 A215, Phone 301-975-6722, Fax 301-975-5449, yes I am a Sigma Xi member


Background: The objective of this work was to elucidate the fate of Bacillus anthracis spores in treated water system biofilms and evaluate commonly used disinfectants for decontamination in the event of a bioterror attack on a public water systems.  Biofilm communities predominate at water/surface interfaces common to nearly all ecosystems including treated water systems and are known to harbor potential pathogenic bacteria. 

Methods: PVC and copper pipe materials were used in either a continuously stirred tank reactor (CDC reactor) for controlled shear or a pipe loop system.  Native water system biofilms were accumulated on pipe material surfaces with synthetic water containing humic acids as a carbon source.  Once the biofilms were established, Bacillus thuringiensis (kurstaki and ATCC 33679, used as simulants) or Bacillus anthracis Sterne spores were added to the water system.  Pipe surfaces were studied for biofilm accumulation and spore adhesion.  Sodium hypochlorite and monochloramine disinfection of spores in solution and adhered to and biofilm organisms on the pipe materials were quantified using plate count methods. 

Results: Heterotrophic plate counts and biofilm organisms (identified by fluorescent microscopy FISH images) were consistent with literature reported values for drinking water systems.  Spore retention was proportional to the biofilm accumulation (R2 = 0.955).  Biofilms decreased with both sodium hypochlorite (free chlorine) and monochloramine (MC) efficacy over a range of disinfectant concentrations (2-100 mg/L) tested.  MC was more effective at eliminating biofilms and spores from pipe surfaces, however, free chlorine was more effective a free spore disinfection.  High shear and PVC pipe surfaces resulted in larger spore adhesion to the biofilms than copper and low shear.

Conclusions: Biofilms have a large impact on the disinfectant efficacy and may have large implications for the fate of B. anthracis spores in water systems.