Study On Formation And Inhibitor Of Mixed Species Bacteria Biofilm In Milk

Biofilm is a structured consortium of bacteria embedded in a self-produced polymer matrix consisting of polysaccharide, protein and DNA to resist to the detrimental condition. In food processing, biofilm is the most harmful enermy which brings unparallel issues of food spoilage and food contamination. Many researchs aimed at the biofilm consist of one kind of bacteria, which confirmed the quorum sensing weighs heavily in the formation of biofilm. While seldom researchs concern the microbial community structure and the relationship of bacterium in the mixed biofilm. Thus, our research aimed at the influence of different food spoilage condition on biofilm and the relationship of bacterium in the mixed biofilm to find the key of the biofilm formation. Meanwhile, we also discussed the possibility of fruit extracts regarded as the natural inhibitor of biofilm. Our research would deepen the understanding of biofilm and do good to find a effective natural inhibitor in food processing, which would also lay a foundation of controling milk spoilage and biofilm.We investigated the the mixed biofilm(Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella and Escherichia coli) formation ability in different food spoilage conditions and conpared the difference between biofilm formation ability consisted of one kind bacteria and mixed biofilm formation ability. The the relationship among the biofilm formation ability, the viable count in the biofilm and the AI-2activity of mixed biofilm were also studied. With the result of bacterial supernatant influencing biofilm formation ability and three kind of natural product (teapolyphenols, citral and cinnamaldehyde) we analysised the influence of AI-2on biofilm. At last we discussed the possibility of fruit extract acting as the natural inhibitor to biofilm in food processing. The main results were as follows:1. By the method of microtitreplate we have known the relationship of the biofilm formation ability of Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella, Escherichia coli and mixed biofilm is mixed biofilm> Staphylococcus aureus> Pseudomonas aeruginosa>Escherichia coli>Salmonella. We also confirmed the mixed biofilm growed best by the inoculation proportion of1:1:1:1and in the condition of30℃for3days.2.According to plate colony counting, we found the viable count changed every day in the biofilm. Then activity of AI-2in different incubation time was measured by V. harveyi BB170bio luminescence, showed that the minimum AI-2activity was in the2nd day which is only17pers of the first day and the max AI-2activity was in the3rd day which is the2.28times of the first day. Also, the significant correlation was proved among biofilm formation ability, AI-2activity and the viable counts of mixed biofilm.3.We confirmed the supernatant of Staphylococcus aureus promoted the biofilm formation of E.coli to be2times as normal, which proved the bacterial supernatant would increase the biofilm formation of all three kinds of isolates. Then the results of biofilm formation and AI-2activity of these three food-borne pathogenic bacterium and mixed isolates at the subinhibitory concentration of the three nature products indicated teapolyphenols citral and cinnamaldehyde obviously inhibited the biofilm formation of three food-borne pathogenic bacterium and mixed isolates. Biofilm inhibition effect of teapolyphenols on staphylococcus aureus was the best and cinnamaldehyde is the most effective product to inhibit the biofilm formation of E.coli and salmonella. Besides, Citral could inhibits the AI-2activity of all isolates.4.Adding the gradient concentration of furanone in the mixed biofilm proved the inhibiting effect of furanone aimed at the bacterial concentration in the biofilm without the floating bacteria. And the most effective inhibitor in all fruit is the pawpaw extracts which inhibited37pers of biofilm formation and32pers of AI-2activity, while the least effective inhibitor is the orange extracts which inhibited only16pers of biofilm formation and23pers of AI-2activity.