DIRECT MICROSCOPIC COUNT

Despite being quick, this method requires a minimum cell density of 10 cells per mL due to the low sample volume of the counting chamber (Splittstoesser, 1992). Because of this limitation, these techniques find 

Another difficulty with the direct microscope count is the fact that the method views both viable and nonviable (dead) cells. Depending on stage in the growth cycle, as well as history of the sample, the ratio of viable to nonviable cells may vary considerably and makes comparing results to those of direct plating difficult. Because of this, plating normally provides lower estimates of viable populations than microscopy. To make the distinction between viable and nonviable cells, various stains and dyes can be used either singly or in combination (Section 14.4.2, 14.4.3, and 14.4.4). 

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The direct microscopic count determines the number of viable and dead microorganisms ia a milk sample. A small amount (0.01 mL) of milk is spread over a 1.0 cm area on a microscope sHde and allowed to dry. After staining with an appropriate dye, usually methylene blue, the sHde is examined with the aid of a microscope (oil immersion lens). The number of bacterial cells and clumps of cells per microscopic field is determined and, by appropriate calculations, is expressed as the number of organisms per milliliter of sample. 

Because physiological deterioration is generally accompanied by an increase in bacterial population, as pointed out by Nielsen, Wolford, and Campbell (33), estimation of bacterial numbers might serve as the basis of a test for condition. Obviously, the plate count method is not adaptable because of the time limitations imposed. Direct microscopic count would be much more appropriate, especially if a positive field count were substituted for cell count as suggested by Wolford (39). 

An increase in bacterial population would indicate a fermentation of some sort. However, measuring bacteria by plate count is cumbersome, and direct microscopic count in wine is difficult because of the similar appearances of bacteria and grape debris. 

Coulter Counter To avoid the tedium of direct microscopic counting, a Coulter counter can be employed. By using this technique, not only the cell number, but the cell size can be measured. The disadvantage of this technique is that it cannot distinguish between cells and any impure particles. The technique is also difficult to use with organisms in chains and is useless with mycelial organisms. 

Measuring the Soil Microbial Biomass 10.2.3.1 Direct Microscopic Counting... 

A direct microscopic count of the particles was carried out using the Fuchs-rosenthal chamber [15]. Most probable number of Cu(0H] particles (P[vj) contained in 1 mm in the presence of DBS, at pH 8, = 4.72 mmol/dm and... 

Direct microscopic counting (using Helberor haemocytometer counting chambers)... 

Fig. 5.7 Depth distribution in the seabed of microorganisms enumerated by direct microscopic counts of cells stained by a fluorescent DNA stain. The graph shows the global data from ODP cores in a double-log plot, from the sediment surface to 800 m subsurface. Data from Parkes et al. (2000).

The concentration of bacterial inoculum giving suitable results may be determined using direct microscopic count, viable counts, turbidity tubes, or spectrophotometric methods. These methods may not give the same result so one standard method should be used (see Chapter 5). Spectrophotometric methods may produce varying results between species due to differences in the size of the cells and hence their light scattering properties. Each species should therefore be checked. 

Direct microscopic count per gram is Prudhoe crude oil is utilized. 

Direct microscopic count A method of measuring bacterial growth by counting cells in a known volume of medium that fills a specially calibrated counting chamber on a microscope slide. 

Splittstoesser, D.F. 1992. Direct microscopic count. In Compendium of Microbw-logical Methods for the Examination ofEoods. C. Vanderzant and D.F. Sphttstoesser (Eds.), 3rd edition. Chapter 5, pp. 97-104. American Pubhc Health Association, Washington, DC. 

To date, there is only one report on the use of immobilized fungal cell for the production of ethanol [113]. Two mould cultures, Mucor sp. and F.lini were compared with S. cerevisiae for their ethanol producing ability. Inunobilization was attempted as a means to increase the volumetric rate of ethanol production. Spores of Mucor sp. were entrapped in alginate gel. The size of the alginate pellets was 2.5 mm diameter with a cell density of 0.33 g ml. A spore population of 10 was measured by direct microscopic count. F. lini was grown upon the ground corn cobs (3.2 mm diameter). In shaken flasks, both fungal cultures produced ethanol from 10% xylose at lower rates compared to S. cerevisiae which had the best ethanol production rate, 0.3 g 1 h . ... 

Two methods are commonly employed in determining the degree of bacterial contamination of a sample of material (1) the plate method, and (2) the direct microscopic count. 

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