Resistance of Listeria monocytogenes biofilms to disinfectants 326

We studied the optimal conditions for the biofilm development by Listeria monocytogenes on a model system represented by microtiter plates, and also for determined some effective disinfectant agents. Listeria monocytogenes ATCC 13932 and an industrial isolate of Listeria monocytogenes Lm-24 were compared as to their abilities to form biofilms. The starting concentration of the cells leading to the most reproducible results was 0.5 McFarland. The temperatures tested ranged between 8°C to 37°C, the optimal values to form biofilm in buffered peptone water (BPW) with 0.05% glucose were 25°C and 30°C. Under comparable conditions the persistent strain L. monocytogenes Lm-24 constituted more massive biofilm than did the reference strain. The following disinfectants were applied: Savo, Merades Alco, benzalalkonium chloride. A persistent industry in isolate Listeria monocytogenes Lm-24 was used as the model organism for these tests. Benzalalkonium chloride treatment was found to be the most efficient way to damage the biofilm. One minute treatment with 500 mg/l was lethal for the biofilm cells, and that with 125 mg/l for planctonic cells. Savo suppresed the viability of the biofilm cells only by about 20% on average while being lethal for planctonic cells. Merades Alco exhibited only a weak effect on both the biofilm and planctonic cells.