Center for Biofilm Engineering

Abstract:  

"A Repeatable Laboratory Method for Testing the Efficacy of Biocides Against Toilet Bowl Biofilms" 

Methods & Results: A microbial biofilm reactor system incorporating intermittent flow and nutrient provision was designed. The reactor system was open to the air and was inoculated with organisms collected from toilet bowl biofilms. Once an hour, reactors were supplied with a nutrient solution for a period of five minutes, then flushed and refilled with tap water or tap water amended with chlorine. Quantitative measures of the rate and extent of biofilm accumulation were defined. Biofilm accumulated in untreated reactors to cell densities of 10⁸ cfu/cm² after approximately one week. Biofilm accumulation was also observed in reactors in the continuous presence of several milligrams per liter of free chlorine. Repeatability standard deviations for the selected efficacy measures were low, indicating high repeatability between experiments. Log reduction values of viable cell numbers were within ranges observed with standard suspension and hard surface disinfection tests. Biofilm accumulated in laboratory reactors approximately seven times faster than it did in actual toilet bowls. The same ranking was achieved in tests between laboratory biofilms and field-grown biofilms with three of the four measures, using three different concentrations of chlorine.

Conclusions: This reactor system has been shown to simulate, in a repeatable way, bacterial biofilm accumulation that occurs in toilet bowls. The results demonstrate that this system can provide repeatable assays of the efficacy of chlorine against those biofilms.

Significance and Impact of the study: The laboratory biofilm reactor system described herein can be used to evaluate potential antimicrobial and anti-fouling treatments for control of biofilm formation in toilet bowls.

Pitts, B., A. Willse, G.A. McFeters, M.A. Hamilton, N. Zelver and P.S. Stewart, "A Repeatable Laboratory Method for Testing the Efficacy of Biocides Against Toilet Bowl Biofilms," J. Appl. Microbiol., 91:110-117 (2001).