Response of microbial populations

Alzamora, S.M., Guerrero, S., Viollaz, P.E., and Welti-Chanes, J. Experimental protocols for modeling the response of microbial populations exposed to emerging technologies some points of concern. Novel Food Processing Technologies, G.V. Barbosa-Canovas, M.S. Tapia and P. Cano, eds., CRC Press, Boca Raton, Florida, pp. 591-608, 2005. 

Response of Microbial Populations to Carbofuran in Soils Enhanced for Its Degradation... 

SALs for terminally sterilized products are substantiated (validated) by extrapolation of measurable responses of microbial populations at sub-process treatment levels to process treatments that ought to be providing the specified nonmeasureabie SALs. Extrapolation can only be justified when a response takes a regular form and can be supported by theory. This is clearly the case for the kinetics of inactivation of microbial populations. 

It is only very recently that organic componnds synthesized by humans have begun to exert a selection pressure upon natural populations, with the consequent emergence of resistant strains. Pesticides are a prime example and will be the principal subject of the present section. It should be mentioned, however, that other types of biocides (e.g., antibiotics and disinfectants) can produce a similar response in microbial populations that are exposed to them. 

Finally, if the metabolism of the chemical results in substantial energy yield and/or cell-building materials, then the microorganism may increase in cell numbers in response. Then, the overall rate of biodegradation will be dictated by the rate of microbial population increase. In these cases, microbial population dynamics, an approach developed by Monod (1949), must be included in our analysis of the chemical of interest. This too will be expanded upon in Section 17.5. 

Exponential inactivation is the basis of the concept of sterility assurance. If the behavior of microbial populations in response to a particular sterilizing procedure is regular and exponential over the region of the survival curve within which their response can be monitored, then the treatments required to achieve SALs of 10 can be extrapolated. 

Factors that control the fate and transport of organic compounds in aquatic systems include photolysis, hydrolysis, sorption, hydrodynamics, and biodegradation. Biodegradation is the least well understood of these processes, primarily because it is difficult to predict the effects of adaptation, or acclimation, of microbial populations in response to specific compounds. 

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

Based on the previous publications, azo dye can be reduced by azoreductase-catalyzed reduction under anaerobic conditions. But still there is a speculation whether bacterial flavin reductases are responsible for the azo reductase activity observed with bacterial cell extracts. In a published report, it is reported that flavin reductases are indeed able to act as azo reductases [24]. Bacteria produce extracellular oxidative enzymes, which are relatively nonspecific enzymes catalyzing the oxidation of a variety of dyes. It was reported that so many diverse groups of bacteria play a role in decolorization. It has been also reported that mixed microbial community could reduce various azo dyes, and members of the y-proteabacteria and sulfate reducing bacteria (SRB) were found to be prominent members of mixed bacterial population by using molecular methods to determine the microbial population dynamics [1],... 

By now, it has not been made possible to determine the levels of antimicrobials that can cause an increase of primarily resistant Enterobacteriaceae in the gut of the consumer. As a result, measuring the microbial significance of antimicrobial residues continues to be the subject of considerable discussion. Much of the discussion involves the development of model systems that will reflect the effects of residue levels of antimicrobials on human intestinal microbial populations. The consensus of opinion at a recent symposium is that no such single system is available (64). The human intestine is a very complex microbial ecosystem, about which little is known of the effects of antimicrobial residues on the population dynamics and biochenoical responses (65). 

Fig. 6 Evolution of microbial catabolic potentialities during a "summer" type microcalorimetric response to eutrophication. The five bar charts characterize the specialization of the bacterial population, expressed as the ability to metabolize a variety of organic substrates (carbohydrates, alcohols, amino acids etc.).

The initial concentration of the microbial population and the chemical somewhat affects the importance of the last condition and a lag period often occurs between addition of a chemical and the onset of biodegradation. This lag period, usually attributed to the need for acclimation (Alexander, 1994 Spain and Van Veld, 1983), could result from enzyme induction, gene transfer or mutation, predation by protozoa, or growth in the population of responsible organisms. 

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