Controlling Harmful and Pathogenic (Disease-causing) Bacteria
There are millions to trillions of cells in the human body. We are host to many bacteria. How many? There are ten times as many bacteria as there are human cells!
Many of these bacteria are friendly, but others can be pathogens that are characterized as forming a parasitic relationship with their host. The host typically provides a housing and/or food for the bacteria, as well as a place for the bacteria to reproduce and spread throughout the host population.
When harmful bacteria infect you, your immune system goes to work attacking the invaders. This may result in a fever. Bacteria can cause temporary illness or disease (if your body cells are damaged) as a result of the infection. Some bacteria release toxins that damage tissues and/or our immune systems. One of the most dangerous bacterial toxins is found in Clostridium botulinum. This bacterium produces a lethal neurotoxin at very low doses, causing botulism, which leads to paralysis and possibly death.
Food that is inadequately heated or preserved can contain C. botulinum spores that thrive in vacuum sealed cans or jars. These bacteria may live underneath the soil and be accidentally introduced into the cans during harvest. Home-canned foods prepared inappropriately are the culprit of many cases of botulism each year. There are other sources as well.
The toxins that the invading bacteria make cause most of its ill effects. Examine just a few examples of how bacteria can be pathogenic in our bodies. Which bacteria have used your body as a host?
Control of Bacteria: Before Infection
Many bacterial infections can be prevented. Since bacteria are alive, the same sorts of environmental extremes that would kill our cells would kill bacteria outside of our bodies. Take a look at some of the ways humans prevent bacteria from causing us problems.
- Pasteurization – uses heat
- Sterilization – uses heat
- Antimicrobial chemicals – damage the cells of the microorganisms
- UV Radiation – break chemical bonds killing microorganisms
- Frequent Hand Washing
Antibiotics: Controlling Bacteria After Infection
Antibiotics are chemicals that are used to treat bacterial infections by killing or inhibiting the growth of bacteria. Antibiotics can harm bacteria by interfering with their growth, DNA replication, cell wall, enzymes, or even protein synthesis. Antibiotics can also vary in how specific or broad their reach is. Broad spectrum antibiotics, like Amoxicillin, can kill a number of types of bacteria, provided they are not already resistant. Other antibiotics are specific to gram negative or gram positive bacteria.
Alexander Fleming, a Scottish-born scientist, discovered one of the first mass-produced antibiotics, Penicillin almost accidentally. Watch the video, “The Discovery of Penicillin” below and answer the questions that follow to check your learning.
Look for answers to these questions as you watch.
- What world event inspired Fleming to conduct his research experiments?
- Why were soldiers especially prone to infection?
- What stroke of luck set Fleming up for the discovery of Penicillin?
- Where does Penicillin come from?
- What does the Penicillin affect in bacteria?
- Why did Fleming give up his work on penicillin?
- What next steps do you think had to occur before penicillin was used regularly to combat infection and disease?
Stop and Think: Why is Penicillin not harmful to humans or other animal cells? Hint: Think about the ways in which antibiotics attack bacteria. (Answer: It attacks cell walls and animals don’t have cell walls.)
Modern antibiotics are tested in a manner similar to Alexander Fleming’s discovery. Paper disks are soaked in different antibiotics and set on agar where one species of bacteria are growing. This can be used to test hypotheses about which bacteria are most effective:
Kill zones (or zones of inhibition, ZOI) develop around the antibiotic disks (A-E), showing where the antibiotic is effective at killing the bacteria already present on the petri dish. Kill zones can be measured to quantify the effectiveness of antibiotics.
Stop and Think: Which of the paper disks is most effective at killing the bacteria on the petri dish? Which is the least effective? (Answers: E, B)
Benefits of Bacteria
Although many bacteria are pathogenic and a reason to be concerned and vigilant about infections, a great deal of other bacteria species are beneficial for humans and for the environment.
To summarize, bacteria are beneficial in all of the following ways:
Ecological Benefit: Bacteria are decomposers that help the ecosystem recycle nutrients by breaking down dead matter into simpler substances. Bioremediation is a process where bacteria are used to clean up waste, water, oil spills, or convert garbage to compost. Nitrogen fixing bacteria can convert gaseous nitrogen from the atmosphere into a form such as nitrates or nitrites that can be used by other organisms. These bacteria can be used in place of chemical pesticides as part of biological pest control. Bacillus thuringiensis (or BT) pesticide attacks certain caterpillar pests.
Food Industry: Fermented products include yogurt, cheese, sour cream, pickles, alcoholic beverages, buttermilk, sauerkraut (fermented cabbage), and sourdough bread.
Animal/Bacterial Symbiosis: Bacteria that live in the human large intestine produce Vitamin K, which helps in blood clotting. Bacteria living in the stomachs of ruminant animals (cows, rabbits, etc.) assist in the digestion of cellulose.
Industry: Bacteria are used to produce medicines (insulin) or other useful compounds. Bacteria are model organisms for biology research laboratories (they are easy to grow).