Solidified Media

When necessary, liquids may be made solid by the inclusion of agar at 1.5-2% (wt/vol). Agar is a complex polysaccharide prepared from seaweed. It is not utilized by bacteria/yeast and, at temperatures 45° C (113°F), maintains the medium in solid form. Solidified media may be prepared and poured after autoclaving as plates, as slants (slopes), or as agar deeps. Preparation of each is described as follows  

Recently autoclaved agar (in flask or test tubes) equilibrated to 50-55°C (122-131°F) 

After disinfecting the work area, position six or more sterile petri plates near the edge of the bench. 

Holding the flask (or test tube) in one hand, remove the stopper and flame the flask s mouth. 

Carefully lift the cover of the Petri plate high enough to permit pouring agar. Pour 12-15 mL of sterile liquified agar into the plate. Immediately replace the cover, reflame the flask s mouth, and restopper. 

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To inoculate, place a filter on top of solidified media m a Petn dish and spread an appropriately diluted bacterial culture over the surface. 

Agar solidifies media - it is made from red algae Gelidium (Rhodophyta). Chemically it is mostly comprised of galactose and very few microbes can degrade it. It remains liquid at 100 °C (easy to pour) and solidifies at 40 °C (incubation temperatures). 

Wc have tabulated the r( sults of all surface and depression ti sts for pollen tube chemotropism that were made using gynoecia or gyiioccial parts, i.c., stigma, style, ovary wall, ovules. The restriction oii the ba.sis of iiK tliod excludes only the viTy rarly work of Van Tieghem (1809) and. Strasburgor (1878), both of whom worked with solutions rather than solidified media. They came to opposite conc,lu,sions. 

Substances that solidify media for forest trees are most frequently Phytagel and less frequently agar - natural extract from red alj e. The concentration of these substances in the medium is important for the correct development of callus. Too high concentration hinders diffusion, and hence reduces the availability of nutrients for cells, while too low concentration favors the occurrence of "vitreous" explants i.e. callus is too hydrated, it is characterized by anatomical and physiological anomalies. Genus Finns is an exception... 

When grown on solidified media (Section 13.5), colonies appear white to yellowish and may be glistening, moist and smooth, or dull and... 

Species of Dekkera/Brettanomyces produce large amounts of acetic acid when grown on glucose (Freer, 2002). In fact, acetic acid production can be sufficient to inhibit and eventually kill cultures maintained on unbuffered media. Thus, routine laboratory maintenance media contains 2% w/v calcium carbonate to buffer against the acids produced (Section 13.5). However, Brettanomyces tends to a slow growing yeast, often requiring several days for colonies to appear on solidified media. 

Drying ovens should never be used to re-melt solidified agar media because too much water will evaporate from the medium. Re-autoclaving media for a complete sterilization cycle will also degrade heat-sensitive nutrients in the medium. Rather, solidified media can be melted by placement in a boiling water bath or a microwave, the later performed with hand mixing every few minutes. 

Hockey stick A glass rod bent into the shape of an L that is used to evenly spread samples onto solidified media. 

Petri plates or dishes Sterilized glass or plastic dishes with covers that are used to hold solidified media. 

Various means of particle identification are possible with optical microscopy. These include dispersion staining for identification of asbestos particles [44] and the use of various mounting media [45], Proctor et. al. [46,47] dispersed particles in a solidifying medium of Perspex monomer and hardener. This was poured into a plastic mold that was slowly rotated to ensure good mixing. Microscope analyses were carried out on thick sections a lower size limit of 5 p,m was due to contamination. 

Photochemistry of previtamin D (41 see also Special Topic 6.4) is an example of E Z isomerization in trienes. Thermal (A) interconversion of its conformers 41a,b is suppressed in a cold, rigid matrix of a solidified medium (92 K) (Scheme 6.8). Upon irradiation, 41a isomerizes to the thermodynamically more stable tachysterol conformer 42a, whereas 42b is formed exclusively from the conformer 41a. 

A number of different methods for the determination of bacteria in market milk have been devised. The oldest and most widely practiced is tire plate method of Koch. This method is carried out by adding a known amount of milk to a medium which solidifies upon cooling on a plate. When this solidified medium is incubated each bacterium or clump of bacteria multiplies and becomes a colony visible to the naked eye. These colonies are counted and constitute the plate count when proper consideration is made for the amount of milk plated. 

Agar A polysaccharide extracted from certain marine algae and used to solidify medium for the growth of micro-organisms. 

To prepare a solidified medium, add 20 g agar prior to autoclaving at 121°C/250°Ffor 15min. 

When an aliquot of grape must or wine is placed on a suitable solidified medium, colonies of various morphologies will appear on the plate. In theory, a single viable cell in the original sample continuously multiplies to eventually yield one visible colony after a suitable incubation. 

Microorganisms are commonly stored on the appropriate solidified medium, either as slants or stabs (weeks) or for longer periods (months) as liquid cultures suspended in glycerol kept at low temperatures (—70°C/ —94°F). Alternatively, microorganisms can be preserved for very long term storage (years) by freeze-drying. Method 13.10.3 has been used to freeze-dry yeasts (C.M.L. Joseph, personal communication, 2005), and method 13.10.4 has been used successfully for lactic acid bacteria (Duke, 1979). 

Certain yeast strains, known as killer strains (K), secrete proteinic toxins into their environment that are capable of killing other, sensitive strains (S). The killer strains are not sensitive to their toxin but can be killed by a toxin that they do not produce. Neutral strains (N) do not produce a toxin but are resistant. The action of a killer strain on a sensitive strain is easy to demonstrate in the laboratory on an agar culture medium at pH 4.2-4.7 at 20°C. The sensitive strain is inoculated into the mass of agar before it solidifies then the strain to be tested is inoculated in streaks on the solidified medium. If it is a killer strain, a clear zone in which the sensitive strain cannot grow encircles the inoculum streaks (Figure 1.17). 

The agar [9002-18-0] plate method consists of adding a known quantity of sample, usually 1.0 or 0.1 mL, depending on the concentration of bacteria, to a sterile petti plate and then mixing the sample with a sterile nutrient medium. After the agar medium solidifies, the petti plate is incubated at 32°C for 48 hours after which the bacterial colonies are counted and the number expressed ia terms of a 1 mL or 1 g sample. This procedure measures the number of viable organisms present and able to grow under test conditions, ie, 32°C. 

As a growth medium, agar has nice properties, such as a high melting point (85°C), and a lower solidifying point (40°C). It can stay... 

Chthoniobacter flavus has been obtained in pure culture (Sangwan et al. 2004), which was made possible by the use of a dilute nutrient broth medium solidified with gellan gum in place of agar (Janssen et al. 2002), and this has since been extended (Sangwan et al. 2005). 

The typical cream, a soft, emulsified mass of solidified particles in an aqueous, micelle-rich medium, does not form a water-impermeable (occlusive) film on the skin. Nevertheless, creams contain lipids and other moisturizers that replace substances lost from the skin in the course of everyday living. Creams thus make good emollients because, by replenishing lipids and in some instances also polar, hygroscopic substances,... 

There is no need to adjust pH. Solidify this medium with 0.15% gellan gum. 

The frozen-drop technique was naturally adopted in measuring molten metal droplet size before any other methods became available. Similarly to the methods for normal liquids, the freeze-up and collection of molten metal droplets may be carried out in many different ways. For example, metal droplets can solidify during flight in gaseous or liquid medium in a spray chamber. 13H51 The solidified particles are subsequently sieved to obtain the size distribution. 

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