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Controlling Growth

Microbiologists are continually altering physical and chemical conditions to modify microbial growth.  Sometimes the intent it to maximize the growth rate so the microbes can be studied.  Other times the intent is to slow or stop growth so that foods don't spoil or infections go away.  Controlling growth is important in either instance.

Scientists will use incubators or growth chambers or fermenters to maximize the growth rates of their cultures.  Speeding up growth speeds up identification and harvesting of valuable growth products.  Commercial enterprises and consumers will use freezers and refrigerators to slow down or stop growth so products have longer "shelf life" and remain wholesome for consumption.  Heat is used to cook foods and kill any contaminating bacteria that could pose a health threat.  Our ability to control the temperature of growth has huge advantages.

Besides manipulating temperature, other methods are used to control growth, particularly through the addition of chemicals.  Ever wonder why potato chips can be held at room temperature but potato salad can't?  Why apple cider vineagar can sit in the cupboard but apple juice must be refrigerated?  The reason is because of the general chemical condition of the foods.  The oldest methods of preserving foods are drying and salting.  In either process, water is removed from the cells of contaminating microbes thereby preventing growth.  Without water in the cells, metabolism cannot occur.  Without metabolism, the microbes cannot spoil or taint food.  In the case of vineagar, the acidification of the apple cider results in a growth condition where few bacteria can grow.  Drying, adding salt, and acidifying are major strategies used for improving the stability and safety of foods.

This is not the answer for all foods or consumer products.  Sometimes, other chemicals must be added to slow or prevent growth.  These preservatives increase shelf life and thus make products easier to ship and more longlasting in the marketplace.

But controlling microbial growth is not restricted to foods and spoilage.  We use soap and water and floss and brush our teeth.  We use antibiotic ointments and mouthwashes.  We disinfect our toilets and floors.  All of these and countless other actions are taken to prevent rampant microbial growth that could cause disease.  And scientists take advantage of chemical additives to bacterial growth media to select wanted bacteria while preventing the growth of contaminants.  Each time we modify a growth environment's temperature or chemistry to improve or retard growth, we are practicing selective measures against microbes.

In this section, we will look more closely at methods for controlling growth of microbes