Study on biofilm formation of bacteria isolated from cucumber fruits

The characteristics of bio films of nine kinds of bacteria isolated from cucumber fruits were investigated. The biofilms of a single bacterium developed on the inner surface of a polystyrene test tube within 2 days of culturing in four nutrient levels of trypticase soy broth (TAB; 1:100, 1:50, 1:20, and fresh broth) at 5 and 25°C. Biofilm formation was evaluated by the OD ₅₀₀ of bacterial suspension stained with 0.1% (w/v) of crystal violet solution. Two isolated bacteria developed stronger biofilm on polystyrene surface with all the four nutrient levels at 25°C. When all the nine bacteria were cultured together in one test tube, the strongest bacterial adhesion was observed in the 2 days culture using any of the four nutrient levels. Culturing two bacteria which demonstrated stronger bio film in one test tube resulted in a weaker biofilm compared to that of the individual bacterium. However, considerably stronger bio film developed by the incubation of a bacterial cocktail of the seven isolates, which had developed weak bio films. In addition, bio film developments of a bacterial cocktail of the seven isolates were considerably enhanced in the diluted TAB in comparison with the fresh broth. This result indicated that the development of bio film containing different species of bacteria could be affected by the specific bacteria-bacteria or bacteria-metabolite interaction involved in some physiological (genetic) responses to the poor nutrient (stressful) conditions.