The colonies developed along the spiral pathway can be counted either manually or electronically. After the liquid containing microorganisms is spread, the agar plate is incubated overnight at an appropriate temperature for the colonies to develop. The volume of liquid deposited at any segment of the agar plate is known. The Spiral Plating system (Spiral Biotech, Bethesda, MD) can spread a liquid sample on the surface of nutrient agar in a Petri dish automatically in a spiral shape (the Archimedes spiral) with a concentration gradient starting at the center and decreasing as the spiral progresses outward on the rotating plate. These new methods were first designed to perform total viable cell counts but more recently due to improvements of media development and additional tests these methods can also detect and enumerate pathogens such as Salmonella, E. Several ingenious methods have been developed to make the viable cell count more efficient, automatic and cost effective. Although this time-honored procedure is practised all over the world, it is time-consuming, labor intensive, and wasteful of glassware and large numbers of disposable items, such as plastic pipettes and Petri dishes. After solidification of the agar, the Petri dishes are then placed into the incubator at the desired temperature, for example, 32 ☌, 35 ☌, or other temperatures for microorganisms, to grow to visible colonies, usually 24–48 h before counting the number of colonies and converting the number in counts per milliliter or per gram of the food. Then the diluted liquids are accurately pipetted into a sterile Petri dish (usually 0.1 or 1 ml) and then melted nutrient agar (48 ☌) is poured into the Petri dish. It involves preparing food into a slurry and then serially (1:10 series) diluting it to a final desired concentration of somewhere between 1:100 and 1:1 000 000 depending on the estimated concentration of microbial population. The conventional viable cell count or standard plate count method has been in use for more than a century. Fung, in Encyclopedia of Food Microbiology (Second Edition), 2014 Alternative Methods for Viable Cell Count Procedure
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