title: A repeatable laboratory method for testing the efficacy of biocides against toilet bowl biofilms.
abstract: OBJECTIVE
  The purpose of this study was to develop a laboratory biofilm growth reactor system that simulated the toilet bowl environment and which could be used for biocide efficacy testing.
  
  
  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 per hour, reactors were supplied with a nutrient solution for 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 biofilm accumulation were defined. Biofilm accumulated in untreated reactors to cell densities of 108 cfu cm-2 after approximately 1 week. Biofilm accumulation was also observed in reactors in the continuous presence of several milligrams per litre 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, the accumulation of bacterial biofilm that occurs in toilet bowls. The results demonstrate that this system can provide repeatable assays of the efficacy of chlorine against those biofilms.
  
  
  CONCLUSIONS
  The laboratory biofilm reactor system described herein can be used to evaluate potential antimicrobial and antifouling treatments for control of biofilm formation in toilet bowls.
authors.affiliation: Center for Biofilm Engineering, Department of Chemical Engineering, Montana State University, Bozeman, MT 59117, USA.
authors.forename: B
authors.initials: B
authors.lastname: Pitts
authors.forename: A
authors.initials: A
authors.lastname: Willse
authors.forename: G A
authors.initials: GA
authors.lastname: McFeters
authors.forename: M A
authors.initials: MA
authors.lastname: Hamilton
authors.forename: N
authors.initials: N
authors.lastname: Zelver
authors.forename: P S
authors.initials: PS
authors.lastname: Stewart
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects / Q000254:growth & development; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D019149:Bioreactors / Q000382:microbiology*; D002713:Chlorine / Q000494:pharmacology*; D003627:Data Interpretation, Statistical; D008954:Models, Biological; D012107:Research Design; D014038:Toilet Facilities
chemical_list: D000900:Anti-Bacterial Agents; D002713:Chlorine