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Aims: The purpose of this study was to develop a laboratory bio®lm growth reactor system that simulated the toilet bowl environment and which could be used for biocide ef®cacy testing. Methods and Results: A microbial bio®lm reactor system incorporating intermittent¯ow and nutrient provision was designed. The reactor system was open to the air and was inoculated with organisms collected from toilet bowl bio®lms. Once per hour, reactors were supplied with a nutrient solution for a period of 5 min, then¯ushed and re®lled with tap water or tap water amended with chlorine. Quantitative measures of the rate and extent of bio®lm accumulation were de®ned. Bio®lm accumulated in untreated reactors to cell densities of 10 8 cfu cm ±2 after approximately 1 week. Bio®lm accumulation was also observed in reactors in the continuous presence of several milligrams per litre of free chlorine. Repeatability standard deviations for the selected ef®cacy 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. Bio®lm accumulated in laboratory reactors approximately seven times faster than it did in actual toilet bowls. The same ranking was achieved in tests between laboratory bio®lms and ®eld-grown bio®lms 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, the accumulation of bacterial bio®lm that occurs in toilet bowls. The results demonstrate that this system can provide repeatable assays of the ef®cacy of chlorine against those bio®lms. Signi®cance and Impact of the Study: The laboratory bio®lm reactor system described herein can be used to evaluate potential antimicrobial and antifouling treatments for control of bio®lm formation in toilet bowls.

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