Or can they make us ill? How do they get in? What is their role in the body? Bacteria are tiny living microorganisms that are too small to be seen by the naked eye. They are a 1, times smaller than a pencil tip. We have to use an instrument called a microscope, which makes the image of the bacteria big enough to be seen.
There are many different kinds of bacteria with diverse shapes and sizes. Some look like a baseball bat, others are round like a basketball but millions of times smaller Figure 1.
Bacteria live on the skin, inside the nose, in the throat, in the mouth, in the vagina, and in the gut. The majority of the bacteria found in the body live in the human gut.
There are billions of bacteria living there Figure 2. We call the group of all the microbes found in the body the human microbiota [ 1 ]. These microorganisms colonize the body, which means that they usually do not cause any harm. When a microorganism causes sickness, that is called an infection.
We begin to be colonized by bacteria during birth. During the birth process and immediately after birth, we get our first microorganisms.
All babies also acquire bacteria from the skin of the nurses and medical doctors and the environment they live in. After babies begin to eat, they get microbes from their diet. In the first days of life, the type of the microorganisms that colonize their intestines will be different, depending whether the baby is breast feeding or drinking formula. As babies grow, they get microorganisms from the solid food they eat, from crawling on the floor, from putting their hands in their mouths, from licking toys, and from many other sources!
The microbes that live in the human body change during our growth, until we are 3 years old. At that point, the microbiota becomes more or less stable until adult life. Each individual has his or her own microbiota, which depends in part, but not only, on the types of food eaten, the environment where the person lives, and the other people and animals that the person interacts with Figure 3 [ 2 , 3 ]. When we mention bacteria in the human body, you might immediately think of a disease, called a bacterial infection.
At some point in your life, you have probably had an infection that was treated by antibiotics prescribed by your doctor. Antibiotics are medicines that kill or prevent the growth of bacteria. However, the majority of the microbes are harmless and actually help to maintain our health.
The microbes of the skin, mouth, and nose fight against bad bacteria that want to enter the body to cause disease. These good bacteria act like guards that keep away the harmful bacteria that make us sick. The bacteria that colonize the vagina are another example of good bacteria. They maintain an acidic environment in the vagina that prevents the growth of other microorganisms that might cause disease. Disease-causing microorganisms are called pathogens.
Even though most of the time they are harmless or even helpful, in certain conditions some of the bacteria that are part of the human microbiota can harm us. For example, bacteria that live on the skin can become a problem.
If you cut yourself, the bacteria that live on the surface of your skin may be able to enter into your body through the cut, getting in where they do not belong. In this instance, these bacteria sometimes might be harmful to the body and trigger an infection. Symptoms of an infection include pain, swelling, redness, and fever. Another example of how the microbiota can harm us is when you let too many bacteria accumulate in your mouth.
These bacteria can stick to the surface of your teeth. Tell students that they will not be able to see streaks on the plate after swabbing. Have students rub inoculate the control dish with a clean, moist swab. Collect used swabs from students and discard as instructed in "Safety Issues. Distribute clean Petri lids or dishes. Ask one group member to prepare an additional sheet for observing the control.
Students should take turns making control observations. Have students observe the cultures daily for 1 to 3 days. If possible, have them use a low power microscope to observe the cultures through the lids of the dishes. Do not allow students to open the Petri dishes. Conduct a class discussion. Ask, What has changed inside the Petri dishes? Molds, which form fuzzy or felt-like colonies, also may be present. Have students decide how many different kinds of organisms might be growing on their gels, based on differences they can observe.
Do not allow students to open the dishes. Some common microorganisms that might be present include fuzzy green Penicillium mold, black fuzzy or hairy bread mold, or various circular white, dark or colored colonies of bacteria. Yeast colonies usually are white. It is not important for students to be able to name all the microbes. On Day 3, have students count the number of colonies, or measure and compare diameters of the colonies on their observation sheets.
Have students decide which sample sources had the most microbes. Have each group prepare a brief summary comparing its observations with its chart of sample locations and predicted results. Have groups share their summaries with the rest of the class. Based on these reports, have students answer the question posed at the beginning of the activity: Are there any microbes in the room? If so, where are they? Also, discuss the multiple roles of microbes in the environment.
Ask, Have you ever seen any colonies of microbes particularly bacteria and molds growing on food, on damp surfaces, or in natural environments? What do you think is happening when microbes grow on something? The microbes are using the substance as a food source. Discuss the important roles of microorganisms as decomposers of dead organic material in ecosystems.
Have students design additional experiments to test for the presence of microbes. They might examine water from different sources, compare washed vs.
Have students investigate what happens when similar samples are grown at room temperature and in the refrigerator. Based on their results, conduct a discussion about the importance of refrigerating leftover food. Students explore microbes that impact our health e. Student magazine: Special issue featuring healthcare professionals who discuss why each chose his or her career, educational requirements needed to obtain the job, and day-to-day responsibilities.
Student magazine: Articles focusing on microbes, both helpful and harmful. What is Science? Slaptail's Curious Contraption Mr. Microbes Are Everywhere Olha Rohulya. Objectives and Standards Inquiry Identify questions that can be answered through scientific investigations. Think critically and logically to make the relationships between evidence and explanations. Recognize and analyze alternative explanations and predictions.
Communicate scientific procedures and explanations. Today kingdom taxonomists have defined systems based on five or six kingdoms Archaea - the sixth, Monera, Protoctista, Fungi, Plantae, and Animalia , neither of which include viruses or prions. Viruses are considered to be on the line between living and non-living.
It has been argued extensively whether viruses are living organisms. Most virologists consider them non-living, as they do not meet all the criteria of the generally accepted definition of life.
For instance, most viruses do not respond to changes in the environment, which is a definitive trait for living organisms. In addition, viruses can replicate themselves only by infecting a host cell. They therefore cannot reproduce on their own. Prions are a recently discovered infectious agent.
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