A fluorescent method for assessing the antimicrobial efficacy of disinfectant against Escherichia coli ATCC 35218 biofilm

In this study, a versatile method was developed to assess biocide efficacy against Escherichia coli biofilm growth on carriers made of five different materials. The glucuronidase activity of live E. coli on a fluorogenic substrate (4-methylumbellyferyl-beta-D-glucuronide, MUG) was used as a viability test. Fluorescence emissions from cellular suspensions of E. coli in the test range displayed a linear response with a MUG concentration of 10 mu g ml(-1). A glucuronidase activity curve with cellular suspensions of E. coli calculated as colony-forming units per milliliter showed a good correlation (0.9487 and 0.917 for 1 and 18 h of incubation, respectively), with counts obtained from biofilm containing this organism; E. coli cultures in suspension were used as standard. Three agents commonly used as disinfectants, sodium hypochlorite, hydrogen peroxide, and ethanol, were tested at use concentrations and at one-half and decimal dilutions. At decimal dilutions, ethanol at 70% proved to be the least active disinfectant on E. coli biofilm. Unlike other methods, our method permits the testing of disinfectant efficacy against biofilm growth on different materials. In preliminary assays, glass, polyvinyl chloride, polypropylene, polycarbonate, and silicon were tested. Because they gave the lowest E. coli counts after 24 and 48 h, glass and polypropylene were the two materials to which biofilm adhered least strongly.