lecture8probioticbacteria：講座8益生菌(存儲版)

　　

【正文】 ple) ? modes of action were largely circumstantial ? several modes of action have been proposed as a result of human and agricultural applications Modes of Action ? Info on terrestrial investigations has been used for aquatics (esp. Lactobacillus sp.) ? one problem: distinction between 1) the intrinsic ability of the probing to positively influence the host and 2) its ability to reach and maintain itself in the location where the effect is to be exerted ? Point: does not matter if it produces siderophores or inhibitory pounds in the gut if it’s never ingested ? can be very important: Mytilus edulis (Blue Muscle) can selectively ingest/digest microbes Modes of Action ? Also, if the candidate probiont cannot proliferate in the gut it probably won’t exert a strong effect ? will need continuous application through the diet or via the water ($$$) ? summary: they must reach the location where effect is desired Possible Modes of Action ? production of inhibitory pounds ? petition for chemicals/available energy ? petition for adhesion sites (exclusion) ? enhancement of the immune response ? improvement of water quality ? interaction with phytoplankton ? a source of macro and micronutrients ? enzymatic contribution to digestion (1) production of inhibitory pounds ? Release of chemicals having a bactericidal or bacteriostatic effect ? ultimate result: petitive edge for nutrients/energy ? production sites: in host intestine, on its surface, or in culture medium ? products: antibiotics, bacteriocins, siderophores, lysozymes, proteases, hydrogen peroxide, anic acids (pH change) ? exact pound is seldom identified: hence, the term “inhibitory” (1) production of inhibitory pounds ? Lactobacillus sp. produces bacteriocins (toxins) ? marine bacteria produce bacteriolytic enzymes against V. parahaemolyticus ? Alteromonas sp. produces monastatin, shown to be inhibitory against Aeromonas hydrophila ? inhibitory effects have been shown by probiotics against aquaculture pathogens ? no demonstration under in vivo conditions (oops!) ? more research required!!! (Didn’t you mention this last time??) (2) Competition for Chemicals or Available Energy ? Explains how different microbial populations exist in same ecosystem ? it is likely that it occurs in the mammalian gut, but proof is lacking ? application of the principles of petition to natural situations is not easy ? microbial situation in ecosystems is usually controlled by heterotrophs peting for anic substrates as both carbon and energy sources ? if you know the factors affecting microbial position of the microbiota, you can manipulate it (2) Competition for Chemicals or Available Energy ? All microanisms require iron for growth ? siderophore: low mw ferric ionspecific chelating agents ? dissolve precipitated Fe and make it available for microbial growth ? siderophores scavenge Fe and make it unavailable to other species ? this occurs at tissue level ? probiotics producing siderophores can outpete pathogens for Fe, thus limiting pathogen growth ? works best with pathogens that also produce siderophor