Most of us have found it valuable to reduce or eliminate microbes at sometime during our life. Whether it was recognizing that we were possibly sick, that the bathroom had an undesirable odor, that our crops or pets were not growing or performing well, or that some object appeared dirty with possible microbes, we decided to investigate the concern and possibly select a substance or activity to prevent microbial growth. Several factors need to be considered before selecting the proper control.

One factor is the environment. Is the area clean or dirty? Living or nonliving surface? What is the pH? The temperature? In addition we also must know the number and type of microbes present. Are the microbes all one type (pure) or a variety (mixed)? Are the microbes viruses, fungi, bacteria? Are the microbes pathogens or not pathogens? Do the microbes possess endospores?

In order to increase the effectiveness of the control, we should clean the surface (environment), reduce the surface tension of the microbe and the control, and modify the pH of the environment to a pH where the control works best. Under ideal conditions a population of microbes is reduced by a constant percentage per time. For instance, if 50% of a population of one million microbes is killed in 2 minutes, then 500,000 living microbes will be left; then 250,000 microbes will be killed in the next 2 minutes; this exponential reduction will continue until 0.5 of a living cell remains. We can never be certain that all microbes have been destroyed unless we increase the concentration or time of exposure to produce a more rapid and complete elimination of the microbes. For example, Salmonella in feces requires a very effective disinfectant like carbolic acid kept in contact the microbe for a long time to effectively kill all the Salmonella.

The relative resistance of microbes to controls varies greatly. Bacterial endospores have the highest resistance and are most difficult to control. Most vegetative or growing bacterial cells, yeasts, and ordinary fungal spores considered the least resistant. The group considered to be moderately hard to control include viruses like hepatitis-B and poliovirus, protozoan cysts, and bacteria like Mycobacterium, Staphyloccocus, and Pseudomonas.

Another factor to consider when selecting a control is the desired effect you want. It is often necessary to have things sterilized. A sterilized object usually has no living microbes capable of reproduction; however, sterilized soil in horticulture means no pathogens present and sterile soil may contain non-pathogenic microbes. Occasionally we desire the elimination of pathogens and use the term disinfecting on non-living surfaces and antisepsis on living tissue. Still other times, we want a surface or piece of equipment to pass inspection; if a chemical was also used in the cleaning process we may call the area sanitary. Sometimes we simply want to reduce or remove some microbes so we "degerm" or "clean" the area. The friction resulting from rubbing alcohol wipes and germicidal soaps mechanically removes potential pathogens and creates antisepsis.

When deciding the action or material to be used to control microbes, I hope you will always consider the effect on the environment. If a chemical is going to be used, check to see if it is biodegradable. Biodegradable indicates that a microbe in the environment has been identified as being capable of decomposing or changing the material back to valuable and useful nutrients. It is also important to consider the potential harm that may be caused by the control on plants, humans, and other animals. The residual – long term effect – lasting effectiveness of the control may be significant in your decision to use or not to use a specific control.

The economics, or cost and availability, are also important. Most of us will select the less expensive control if we can be assured that it is equally effective in reducing or eliminating the microbes. Sale items should be evaluated carefully watching the shelf-life date, the amount to be used, and other instructions regarding the control. Some controls corrosive or staining; and long-term use may damage your equipment or lab. Still other controls may release odors that are both pleasant or offensive. However, do not be tempted into believing a pleasant smell is the same as an effective control.