Microbial antagonism

Sturz, A.V., Carter, M.R., Johnston, H.R. A review of plant disease, pathogen interactions and microbial antagonism under conservation tillage in temperate humid agriculture. Soil Till Res 1997 41 169-189. 

In 1908 Elie Metchnikoff was awarded the Nobel Prize for his work with the lactic acid bacteria (LAB). He reported that populations that ingested soured milk such as the Bulgarians were known for their longevity. He studied intestinal microflora and reported that LAB were beneficial to human health, making him the first scientist to report benefits of these organisms. Since then, numerous scientists have studied not only the health benefits associated with the LAB, but also the concept of microbial antagonism of the LAB toward food-borne pathogens. 

The concept of microbial antagonism or microbial interference has been known for several decades. This concept refers to the inhibition of undesired or pathogenic microorganisms, caused by competition for nutrients, by the production of antimicrobial metabolites (Gombas, 1989 Holzapfel et al., 1995 Hugas, 1998 Hurst, 1973 Jay, 1996 Stiles, 1996) or by various other mechanisms depending on the situation in which the LAB are used. 

Work in gnotobiotic animals has suggested that production of inhibitory substances is at least partially responsible for microbial antagonism, so it is important to select strains that produce antimicrobial products. It is essential to select LAB that have the most potential to produce the desired effect in the animal and then test the LAB in vivo to verify that the strain is effective in the animal. 

Although the concept of microbial antagonism by LAB is not new, the application to farm animals has gained interest only in the past few decades. Inhibition of Salmonella in poultry was the first research area of interest, and LAB have been proven to reduce E. coli 0157 in cattle before slaughter. Reports in the literature vary with respect to the efficacy of LAB in reducing food-borne pathogens in farm animals. It is important to consider the source of the DFM, application of the product, and methods used to evaluate the... 

Hurst, A. 1973. Microbial antagonism in foods. Can. Inst. Food Sci. Technol. J. 6, 80-90. 

Salivary secretions Indigenous microflora Limits microbial proliferation Microbial antagonism... 

Aside from potential sensory implications, acetic acid and associated products of LAB metabolism represent potent inhibitors to fermentatively growing Saccharomyces, delaying the onset of fermentation and potentially causing fermentation to stick (see previous discussion of Microbial Antagonism). At pH >3.5, bacterial carbohydrate metabolism (Peynaud and Domercq, 1968) or MLF (Giannakopoulis et al., 1984 Zeeman et al., 1982) yielded higher concentrations of acetic acid than parallel lots at a lower pH. 

Microbial antagonism The ability of normal microbiota to compete with pathogenic organisms and in some instances to effectively combat their growth. 

S. A. Waksman, Microbial Antagonisms and Antibiotic Substances, Commonwealth Fund, New York, 1945. 

Flash-pasteurization (heating between 72 and 76°C for 20 seconds) seems to be effective. It improves the fermentability of wines with stuck fermentation (Dubemet, 1994). This operation is valid for red, rose and dry white wines and should be carried out before inoculating. Its heating effect can be likened to the effect observed during thermo-vinification (Section 12.8.3). In spite of the destruction of yeasts, the heated musts ferment especially well. The effects of this process merit further study but several explanations can be proposed fermentation by a sole strain avoiding microbial antagonisms addition of nntri-tive elements due to yeast lysis elimination of toxic substances and modification of the colloidal structure. 

The antibacterial substances considered are those which have been well enough characterized either chemically or biologically so that uniqueness is certain. The biology of microbial antagonism has been reviewed by S. Waksman (161) and will not be discussed here. Literature citations have been kept to a minimum, with later publications given preference if they are more complete than the earlier ones or if the compound used in the earlier work was impure. The name selected for each substance is the first one applied to the pure compound or one which makes unambiguous the identity of the active substance. 

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