Microbiological contaminants yeasts

In addition, a number of other components will have a marked effect on the susceptibility of polymer dispersions to microbiological contamination. Jakubowski et al. (1992) studied the influence of raw materials on their susceptibility. By adding various of these to water at in-use concentrations, followed by inoculation with a variety of bacteria, yeasts and moulds isolated from contaminated products, they were able to show that many surfactants, defoamers and other additives were highly susceptible (Table 7). 

Microbiological stabilization of wines is necessary to avoid the many problems that may be caused by microorganisms. Lysozyme does not protect sweet wines from fermenting again or eliminate contaminant yeasts (Brettanomyces), nor is it effective against acetic bacteria, which cause volatile acidity in aerated wines. 

Microbiological aspects of pharmaceuticals are of importance not only to sterile products but to all products, in that gross contamination should be avoided irrespective of how the product is used or administered. Although bacteria, moulds and yeasts constitute the major sources of contamination, pyrogens are also included under this heading. 

One of the key achievements in expanding the pool of the available long-chain PEFA (DHA and ERA) is the isolation of the gene encoding synthesis of A -desaturase from the yeast Mortierella alpina (Michaelson et al., 1998). Obtaining REFA from microbial biomass is justified for economic reasons. Moreover, microbiological oil is cholesterol-free and not contaminated with heavy metals or pesticides. 

Polyene antibiotics are used extensively to control fungal contamination, mainly yeasts and moulds, in microbiological medium, in biological samples from which it is hoped to isolate bacteria, and especially in cell and tissue culture media [551—559]. Polyenes are used in conjunction with benzyl penicillin and streptomycin to suppress microbial contaminants in tissue cultures. 

Bleve, G., Rizzotti, L., DeUaglio, F., Torriani, S. (2003). Development of reverse transcription (RT)-PCR and real-time RT-PCR assays for rapid detection and quantification of viable yeasts and molds contaminating yogurts and pasteurized food products. Applied and Environmental Microbiology, 69,4116-4122. 

Priest, F. G., Hammond, J. R., Stewart, G. S. (1994). Biochemical and molecular characterization of Obesumbacterium proteus, a common contaminant of brewing yeasts. Applied and Environmental Microbiology, 60(5), 1635-1640. 

The ability to transfer colonies from one container to another, without contamination, is crucial to success in the microbiology laboratory and serves as the basis for any subsequent work. The need for transferring cultures varies from raising large populations of yeast and/or bacteria to serve as inocula, to having to identify a troublesome organism. Routine transfer of cultures to fresh media is yet another reason. 

During barrel or tank aging, the wine should be protected from air to avoid both chemical and biological oxidation. In addition to oxidative yeasts, acetic acid bacteria still viable after both fermentations are capable of multiplying in the presence of air. To avoid this problem, the containers (tanks or barrels) should be filled as completely as possible. Topping off should be practiced with a wine of excellent microbiological quality to avoid contamination. An inert gas may also be used to replace the atmosphere present at the top of the tanks. 

Regular monitoring of the microbiological state of the wine to verify sterility. If the viable yeast population increases exaggeratedly and attains 1000 cells/ml, an additional sterilization is effected. This increase of the yeast population (Table 9.6) can be explained by the presence of an excessive residual population in the wine (>1 cell/ml) preventing a sufficient sterihty, or by subsequent contaminations. 

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