Direct plating

By convention, the cell population on a countable individual agar plate must be between 25 and 250 individual colonies (Swanson et ak, 1992), although some microbiologists count plates that contain between 30 and 300 colonies. Thus, a wine sample that contains 10,000 cells per mL must be diluted 1 100 to achieve a population of approximately 100 colonies in ImL of diluted wine in an agar plate. The number of dilutions to be prepared can be estimated using an approximate microscopic count (Table 14.1). 

Both spread and pour plate methods are commonly used for microbial enumeration of juice and wine samples. In fact, commercial kits can be purchased with pre-sterilized and pre-poured agar as well as other reagents and materials so that even the smallest of wineries will have the ability to perform these tests. However, both methods also suffer from logistical and interpretational difficulties. For instance, it is generally necessary to plate 

Number of cells in a microscopic field (lOOOx) Potential population (cells/mL) Estimated dilutions to yield countable plates 

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Antimony, arsenic, bismuth, cadmium, lead, tin and zinc cannot be directly plated by these techniques and should be copper plated. 

The inoculum is directly plated onto the solid medium (to check viability). 

Bronze, copper—tin alloy, electro deposits can be produced in thicker deposits using proprietary brightening additives in the plating solution, especially over a smooth bright substrate. The brightest deposit with better corrosion resistance is attained when bronze is plated over a bright nickel plate. However, direct plating over steel is not an uncommon practice. 

Figure 4 A photograph of the Selec H robot built by The Technology Partnership, Cambridge, UK. This robot maintains between 1 and 50 cell lines, performs passaging, cell counting and viability measurements, and direct plating into microtitre plates for bioassay...

Microbiologic culture studies are useful fc>r bacterial identification, especially when an ocular infection foils to respond to treatment. Cultures are often obtained from the eyelids, the conjimctiva, expressed material from the lacrimal sac, and the cornea. Because preserved ophthalmic anesthetics have a bacteriostatic effect, cultures should be obtained if possible before anesthetic instillation. In the case of corneal sampling, it is necessary to provide topical anesthesia for patient comfort. The anesthetic of choice is 0.5% proparacaine because it causes the least bacterial growth inhibition. To enhance the bacterial yield, sterile preservative-free anesthetic may be used. Samples obtained may be inoculated directly onto soUd media plates (e.g., blood agar). Amies without charcoal transport medium (e g., BBL CultureSwab Plus) appears to be an acceptable alternative to direct plating and has the added benefit of convenience. 

A complicated many-layer structure of foam cells is formed when gas bubbles are sparged into solutions of surfactants. According to [429], each bubble has a two-sided envelope which is a layer of the solvent containing hydrophilic polar parts of surfactant molecules (see Figure 7.2). Nonpolar hydrophobic parts of molecules on the inner surface of the envelope are oriented toward the bubble, and on the outer surface, outward the envelope. Between two cells, each of which is a capsule with envelope, there is a lamella, that is, an interlayer of a complicated structure. In the middle of the lamella, there is a liquid layer that is a continuous phase. On each of two surfaces of this layer, there is a monolayer of the surfactant. The hydrophobic parts ( tails ) of surfactants molecules in each monolayer and the tails of the envelope form two direct plate micellae [413], which separate the envelope and the continuous liquid film at the center. Thus, gas bubbles in foam are separated at least by five distinct layers. The multilayer structure of a foam lamella is well seen in photographs (e.g., see [429], p. 54). This fact is also confirmed by the ladder-type shape of the disjoining pressure... 

The point is that the lamella [429] has a complex multilayer structure (see Figure 7.2). It consists of two boundaries of foam cells, two direct plate micellae [413], and a liquid film, which is a part of the continuous phase of the foam. All in all, the lamella has six parallel adsorption layers. Hence, its modulus of elasticity must be many times larger than that of a simple adsorption layer. 

To examine the adhesion of copper deposits to barrier layers, direct plating on barrier layer was compared between ECD seed bath and an acid copper sulfate bath. The acid copper sulfate bath normally produces powdered deposit with poor adhesion that can be easily washed off with water. ECD seed bath provides a continuous, smooth copper deposit with much better adhesion to barrier layers such as TiN, TaN, and WNx. Table 1... 

Brichta-Harhay, D. M., Arthur, T. M., Bosilevac, J. M., Guerini, M. N., Kalchayanand, N., and Koohmaraie, M. (2007). Enumeration of Salmonella and Escherichia coli 0157 H7 in ground beef, cattle carcass, hide and faecal samples using direct plating methods. /. Appl. Microbiol. 103,1657-1668. 

The enrichment conditions can be, and have been modified in many ways. Temperature, pH-value, salt concentration etc. have been varied. Furthermore, the direct plating technique on solid media has been employed to isolate hydrogen bacteria. 

With and without metabolic activation (S9), by the direct plate incorporation method. 

The traditional method for detection of waterborne microbes is direct plating. Samples may also be filtered either on- or off-line and filters placed directly on the surface of an agar plate. A range of media for the detection of coliforms is available (Table 13.3) and confirmation of thermotolerant E. coli is possible by incubation at 44 C. 

Industrial applications. In zinc electrowinning, zinc is directly plated onto aluminum cathodes while oxygen is evolved at the Pb-Ag anode. Once the zinc electrodeposit reaches a desired thickness, the aluminum cathodes are removed from the cells, followed by either manually or automatically stripping the zinc deposit. On the other hand, molten aluminum is used as liquid cathode during the electrowinning of aluminum in the Hall-Heroult process. 

Such a multistable orientation was observed when a capillary was formed by two mica (sixfold symmetry, three easy directions) or NaCl (fourfold symmetry, two easy directions) plates [80, 81]. The director can be switched from one equilibrium position to the other by an electric field (the azimuthal anchoring energy for 5CB between NaCl substrates was shown to be of the order of 10 erg-cm [80]. 

Splittstoesser (1992) described a method using fluorescent dye (acridine orange) known as direct epifluorescence filter technique (DEFT), a method also applied by Divol and Lonvaud-Funel (2005). Divol and Lonvaud-Funel (2005) used a different substrate, fluoresceine diacetate, which is hydrolyzed by viable cells to form a fluorescent product, fluoresceine. However, Atlas and Bartha (1981) observed that cell population values can differ substantially between (epifluorescence and direct plating) methods (10 vs. 10 CFU), possibly due to the presence of viable-but-non-culturable cells. In addition, Meidell (1987) reported interference... 

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