Pour plate method

Repeat this for each test organism. For positive control use sterile DW instead of sanitizer solution. For negative control use sterile strips. Swab each strip thoroughly with a premoistened Ca alginate swab and place in Lecithin broth (or other suitable neutralizer). Vortex for 30 sec, then perform the usual pour plate method. 

Viable Plate Count A viable cell is defined as one that is able to divide and form a colony. There are two ways of performing a plate count—the spread plate method and pour plate method. With the spread plate method, a volume of no larger than 0.1 mL is spread over the agar surface. With the pour plate method, the sample is mixed with melted agar and poured into a sterile plate. The plate is then incubated until the colonies appear, and the number of colonies is counted. It is important that the number of colonies developing on the plates should be neither too large nor too small. To obtain the... 

If 30 is accepted as the lowest reliable number to count and a pour plate method uses a 1.0-ml sample, it follows that the procedures described above are unsuitable for any sample that is expected to contain <30 CFU ml-1, e.g. water samples where the count may be 1 CFU ml-1 or less. Here, membrane filter methods are used in which a large, known volume of sample is passed through the membrane which is placed, without inversion, on the agar surface. Nutrients then diffuse up through the membrane and allow the retained cells to grow into colonies on it just as they would on the agar itself. 

Pour plate method. An aliquot of the neat or diluted sample is added to a sterile Petri dish and mixed with the selected molten agar medium. When the agar has solidified, the plates are incubated for a predetermined time at the specified temperature. Surface or subsurface colonies will develop in some of the agar plates, which can be counted to provide a quantitative value for the bacterial density of the original sample. They can also be picked for further qualitative study. 

Liquid samples can be analysed directly by the spread plate (A) or the pour plate method (B) but they can also be filtered to retain the micro-organism on a filter which is than placed on the culture medium (C). Suspensions need to be filtrated or centrifuged afterwards the filtrate or the filter can be analysed. Solids (e.g. food) must be minced before filtration. Incubation at a given temperature can be aerobic or anaerobic. The result of the counting will depend on the ability to isolate the target organisms with the best recovery rate. 

Colony counts can also be made using the surface method. In this 0.1 to 0.3 ml water is spread out on the surface of the solidified, sterile agar culture medium in the petri dish with the aid of a sterile spatula (Drigalski spatula). However, this method also results in certain differences from the pour-plate method. 

Compared with the pour plate described above, this procedure utilizes previously sterilized bent glass rods (spreaders or hockey sticks) to distribute a defined volume of sample evenly over the surface of the solidified agar medium. Compared with the pour-plate method, thermal shock is not a problem. However, complete transfer and separation of individual cells to yield separate countable colonies may be a concern. Also, excess moisture present on the agar s surface may result in unexpected colony spread... 

Pour plate method Method used to prepare pure cultures using serial dilutions, each of which is mixed with melted agar and poured into a sterile Petri plate. 

Three methods may be used for the enumeration membrane filtration, plate count, and most probable number (MPN) method. The advantages of the membrane filter method are its low limit of detection (LOD) of < 1 CFU/g or mL and the efficient separation of the micro-organisms from components of the product, particularly antimicrobial agents. For the pour-plate method, the sample is generally 1 10 dissolved in the diluent, and 1 mL of the dilution is mixed with the agar. This corresponds to a LOD of 10 CFU/g or mL. The LOD is sometimes higher (e.g. 100 CFU/g or mL) if the product needs to be further diluted due to microbial inhibition, or lower in case of products with low microbial acceptance criteria. If the spread plate count technique is used the LOD is a factor of ten higher (>100 CFU/g or mL), because only 0.1 mL of the... 

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... 

FIGURE 5. Effects of preincubation on the mutagenicity of aflatoxin Bi (a), B[fl]P (b), and quinoline (c). Strains TAIOO (a, b) and TA98 (c) were used with the preincubation method ( ) and the pour-plate method (O). 

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