SUBSTRATUM TOPOGRAPHY INFLUENCES SUSCEPTIBILITY OF SALMONELLA-ENTERITIDIS BIOFILMS TO TRISODIUM PHOSPHATE

Established (48- and 72-h) Salmonella enteritidis biofilms grown in gl ass flow cells with or without artificial cervices (0.5-, 0.3-, and 0. 15-mm widths) were subjected to a 10% trisodium phosphate (TSP) soluti on under different flow regimens (0.3, 0.6, 1.2, and 1.8 cm s(-1)). Th e abundance of biofilm remaining after TSP treatment, the biocidal eff icacy of TSP, and the factors which contributed to bacterial survival were than evaluated by using confocal laser microscopy and a fluoresce nt viability probe. Biofilm age affected the amount of biofilm which r emained following a 15-s exposure to TSP. After TSP treatment of 48-h biofilms, 29% of the original biofilm remained at the biofilm-liquid i nterface, whereas 75% of the biofilm remained at the base (the attachm ent surface). Following TSP treatment of 72-H biofilms, 27% of the bio film material remained at the biofilm-liquid interface, 73% remained a t the 5-mu m depth, and 91% remained at the biofilm base. Results obta ined using the BacLight viability probe indicated that TSP exposure ki lled at the cells in 48-h biofilms, whereas in the thicker 72-h biofil ms, surviving bacteria (similar to 2% of the total) were found near th e 5- and 0-mu m depths. In the presence of artificially constructed cr evices, an inverse relationship was shown to exist between bacterial s urvival (ranging from similar to 13 to 83% of total biofilm material) and crevice width. This relationship was further influenced by the vel ocity of TSP flow; high TSP flow velocities (1.8 cm s(-1)) resulted in the lowest number of surviving bacteria at the base of crevices (simi lar to 42% survival). Extended time courses demonstrated that after TS P stress was relieved, biofilms continued to grow within crevices but not in systems without crevices. It is suggested that advective TSP fl ux into crevices and through the biofilm matrix was enhanced under con ditions of high flow. These results suggest that the inherent roughnes s of the substratum on which the biofilm was grown and the timing of T SP application are important factors controlling the efficacy of TSP t reatment.