4-1 Why enumerate microbes
Many interesting chemical processes take place in the environment, in our bodies an in the food we eat. In almost all cases microbes play an important roll in these chemical conversions. Here are a few examples
It is worthwhile to understand all of these processes and the microbes involved in them. However, it is also just as important to know the population of microbes carrying out these conversions. Just because a microbe has been found that carries out a process does not mean that it is the major actor on any chemical conversion. It may be at too low a concentration to contribute significantly. Therefore, it is often vital to determine the number of microbes as well as their identity.
There are also many other reasons one might need to known the population of microorganisms in a given sample. For example, determining the rate at which a microbe is killed by UV light or heat requires analysis of the number of viable cells before, and at various times during treatment. In other experiments, it is important to know that you have the right density for a procedure, such as required for transforming a plasmid constructed in vitro into an E. coli strain. Assessment of microbial populations in applied industries is also important. Many food-processing plants will measure the level and type of microorganisms present in their food by doing counts on selective medium. In addition, viable cell counts will be performed when optimizing heat treatments for processing food. Sewage treatment plants will routinely sample and count the microbes present in their treatment systems to insure the correct type and numbers of bacteria are present. The microbial count can be determined using a wide array of techniques. Note that these assays all require somewhat different information and in different time frames, as explained below. In this chapter we summarize some of the more common methods and then do some virtual experiments performing them.[Next]