Assessment of biofilm cell removal and killing and biocide efficacy using the microtiter plate test

Biofilm formation on surfaces has serious economic and environmental implications. Growth of biofilm within a water distribution system can lead to problems such as biocorrosion and biofouling accumulation. To prevent and control these occurrences, it is necessary to use suitable biocides to remove the biofilm and kill biofilm cells. In this study, the genera Actinobacillus, Branhamella, Bacillus, Micrococcus and Acinetobacter were isolated from biofilms formed on brass coupons exposed to a cooling water system. It was shown by the microtiter plate test that a mixed culture of the isolates and a single culture of Acinetobacter sp(2) produced high levels of biofilm formation. A microwell plate technique was applied for assessment of the ability of various biocides to remove and kill mixed-culture biofilm cells and Acinetobacter sp(2), the latter as a single-species biofilm with a high rate of biofilm production. The results showed that the mixed-culture biofilm cells had more resistance to removal and killing by some biocides, such as hydrogen peroxide and sulfathiazole, than the single-species biofilm cells (Acinetobacter sp(2)). Oxidising biocides, such as sodium hypochlorite and hydrogen peroxide, demonstrated a higher potential for biofilm removal and killing compared with non-oxidising biocides (sulfathiazole and glutaraldehyde).