Microbial numbers

High organic matter content is typically associated with high microbial numbers and a great diversity of microbial populations. Organic matter serves as a wardrobe of carbon and energy as well as a source of other macronutrients such as nitrogen, phosphorous, and sulfur. Subsurface soils... 

Exponential growth, however, occurs only for a limited time during the course of the development of a microbial culture with a fixed supply of nutrients. The classic time course of the growth of such a culture is shown in Fig. 5.41 where the logarithm of the microbial density (or alternatively microbial number) is plotted against time. 

Since the direct estimation of microbial numbers by conventional culturing methods is time-consuming and well affected by environmental conditions (18), a simple test for the most resistant enzyme activity is appropriate on a routine basis. If enzyme activity is detected, it can be assumed that the heat treatment was inadequate (4,15). Appropriately, GFPuv can be employed as a BI in thermal processes (blanching, pasteurization, disinfection) at temperatures >75°C for products at pH > 5.5, with the inactivation of GFPuv shown to be directly related to the time of exposure to moist heat and pH. 

Taylor J. P., Wilson B., Mills M. S., and Burns R. G. (2002) Comparison of microbial numbers and enzymatic activities in surface soils and subsoils using various techniques. Soil Biol. Biochem. 34(3), 387-401. 

Working with these five documents is not easy they use different terminology and definitions and have different emphases that in part, may be a function of the 10-year span that encompasses publication dates. All of them are concerned with controlling microbiological contamination that may arise from the environment, from personnel, and from materials and equipment. Some individual standards within these documents may relate to microbial numbers, others to physical characteristics that relate to contamination control. 

Olayinka, A., and Babalola, G. O. (2001). Effects of copper sulphate application on microbial numbers and respiration, nitrifier and urease activities, and nitrogen and phosphorus mineralization in an alfisol. Biol. Agric. Hortic. 19, 1-8. 

Five 60 L polypropylene containers to be used for the preparation and homogenisation were rinsed with ultra pure water, interconnected, provided with a drain tap at the bottom and filled with hydrogen peroxide (30 g kg ) to disinfect. After a contact period of 6 h the hydrogen peroxide solution was circulated in the tanks by pumping continuously for 16 h. The tanks were emptied and rinsed with ultra pure water. Samples of the water and from the walls of the tanks were bacteriologically examined (diluted broth agar medium, 10 days at 25°C). Samples of the rinsing water had typical microbial number concentrations (CFP) [3] of less than 1 cm. For the examination of the walls... 

Formate 2.3 X 10 Note Microbial numbers expressed as MPN soil. <3.0 X 10 ... 

Figure 19.1L Effect of current intensity on microbial numbers during electrolysis with and without electrode shielding. DC, direct current n.d., not detectable (

These methods are by definition slow, taking from 24 hours to 10-15 days depending on the samples being examined. There is therefore considerable pressure to replace them with faster methods in the modern QC laboratory. They do, however, provide a very powerful amplification of microbial numbers, and are able to detect very low levels of contamination. Therefore these methods are still widely used and indeed are statutory requirements for the analysis of a number of products. 

There is a close relationship between dry weight and microbial numbers. Although this method would give a good measurement of micro-organisms, there are serious problems in separating the micro-organisms from the sample, and the preparation time of samples is excessive. 

Several investigators have demonstrated that there is no direct correlation between numbers of SRB and the likelihood that corrosion has occurred or will occur. Jack and coworkers [41] prepared a review of 30 months of electrochemical measurements, weight-loss data, water chemistry and microbiological data for an oilfield waterflood operation in which produced brine was injected to displace oil from the reservoir. They concluded that SRB numbers could be used as an index of biocide performance in these field systems. No other correlations between corrosion measurements and microbial numbers were found. 

A healthy host exists in a state of equilibrium with the gut microbiota and in this way this microbiota contributes to a balanced host immunity, to homeostasis at the intestinal mucosa and to metabolism, while the host provides it with a constant and convenient habitat, and at the same time keeps microbial numbers in check. A disorder in the host—microbiota equilibrium may hapjren where a pathogen enters the host intestine and interacts with both the host and the microbiota. If both these two components (host and indigenous microbiota) are resilient, the balance is restored with a consequent recovery of the intestinal mucosa. A disruption of the intestinal homeostasis is the result of a disturbance of the host—microbiota balance that in extreme cases may lead to the death of the host. If the pathogen acquires a niche for itself among the indigenous bacteria of the gut, it will eventually create a new equilibrium between the host and the microbiota with consequent chronic presence of the pathogen. ... 

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