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Bacterial Growth

Bacterial growth is a function of time. Under the right conditions, an initial

population of bacteria will grow exponentially.

Bacterial Growth

Bacterial growth is also a function of temperature. Within the range of 40°F and

140·F, bacteria will thrive.

Bacterial Growth

As a result, we can define a piecewise function of two variables that account for

different temperatures and can be graphed for different values of t.

Bacterial Growth

Here is an example of both variables at work. Two tomatoes, one refrigerated and

one at room temperature, are observed over several days. The tomato at room

temperature rots, while the other tomato is essentially the same.

Bacterial Growth

This graph is a model for a scenario in which a food item is refrigerated up to time

t0, after which it is brought to room temperature. The food-borne bacteria grow

exponentially after t0.

Bacterial Growth

With listeria the situation is different. This type of bacteria will continue to grow even

when refrigerated.

Bacterial Growth

This results in a different piecewise function.

Bacterial Growth

Let’s look at two situations. In each case a canteloupe is refrigerated with the

understanding that this will keep bacteria from growing. But in one case, the

canteloupe is infected with listeria.

Bacterial Growth

The flat-line graph represents the canteloupe without listeria, while the other graph

shows the dramatic growth for the other canteloupe.

Listeria

• The danger of listeria is that it does its work (growing exponentially) under conditions that we think are having the opposite effect.

Bacterial Growth

For more information on listeria and other harmful bacteria, go to FoodSafety.gov.