A repeatable laboratory method for testing the efficacy of biocides against toilet bowl biofilms

Aims: The purpose of this study was to develop a laboratory biofilm growth reactor system that simulated the toilet bowl environment and which could b e used for biocide efficacy testing. Methods and Results: A microbial biofilm reactor system incorporating inter mittent flow and nutrient provision was designed. The reactor system was op en to the air and was inoculated with organisms collected from toilet bowl biofilms. Once per hour, reactors were supplied with a nutrient solution fo r a period of 5 min, then flushed and refilled with tap water or tap water amended with chlorine. Quantitative measures of the rate and extent of biof ilm accumulation were defined. Biofilm accumulated in untreated reactors to cell densities of 10(8) cfu cm(-2) after approximately 1 week. Biofilm acc umulation was also observed in reactors in the continuous presence of sever al milligrams per litre of free chlorine. Repeatability standard deviations for the selected efficacy measures were ion:, indicating high repeatabilit y between experiments. Log reduction values of viable cell numbers were wit hin 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 i n tests between laboratory biofilms and held-grown biofilms with three of t he four measures, using three different concentrations of chlorine. Conclusions: This reactor system has been shown to simulate, in a repeatabl e way. the accumulation of bacterial biofilm that occurs in toilet bowls. T he results demonstrate that this system can provide repeatable assays of th e 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 antif ouling treatments for control of biofilm formation in toilet bowls.