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5.5: Harmful Bacteria

Difficulty Level: At Grade Created by: CK-12
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Could this organism make you sick?

This bacterium, called Mycobacterium tuberculosis , causes the disease Tuberculosis (TB). These bacteria usually attack the lungs. If left untreated, the infection can be fatal. Many other illnesses, mild and severe, are also caused by certain types of bacteria.

Harmful Bacteria

With so many species of bacteria, some are bound to be harmful. Harmful bacteria can make you sick. They can also ruin food and be used to hurt people.


There are also ways that bacteria can be harmful to humans and other animals. Bacteria are responsible for many types of human illness ( Figure below ), including:

  • Strep throat
  • Tuberculosis
  • Pneumonia
  • Leprosy
  • Lyme disease

Luckily most of these can be treated with antibiotics.

Drawing of the Black Death, caused by the bacteria Yersinia pestis

The Black Death, which killed at least one third of Europe’s population in the 1300s, is believed to have been caused by the bacterium Yersinia pestis .

Food Contamination

Bacterial contamination of foods can lead to digestive problems, an illness known as food poisoning . Raw eggs and undercooked meats commonly carry the bacteria that can cause food poisoning. Food poisoning can be prevented by cooking meat thoroughly and washing surfaces that have been in contact with raw meat. Washing your hands before and after handling food also helps prevent contamination.


Some bacteria also have the potential to be used as biological weapons by terrorists. An example is anthrax, a disease caused by the bacterium Bacillus anthracis . Inhaling the spores of this bacterium can lead to a deadly infection, and, therefore, it is a dangerous weapon. In 2001, an act of terrorism in the United States involved B. anthracis spores sent in letters through the mail.


  • Bacteria are responsible for many types of diseases in humans.
  • Some bacteria can contaminate food and cause food poisoning.
  • Some bacteria have been used as biological weapons by terrorists.

Explore More

Use these resources to answer the questions that follow.

Explore More I

  1. How does infection by the bacteria Salmonella typhimurium begin? Do all bacterial infections start this way?
  2. Do all bacteria ingested make it to the intestines? Why or why not?
  3. What does Salmonella typhimurium compete with in the intestines?
  4. What are some possible effects of infection by Salmonella typhimurium ?

Explore More II

  1. What are the common bacteria that cause food poisoning?
  2. What steps can you take to keep your food safe?


  1. What are three examples of diseases caused by bacteria?
  2. How can you prevent food poisoning?
  3. How are bacterial diseases treated?




Medicine that kills bacteria and cures bacterial infections and diseases.
food poisoning

food poisoning

Illness resulting from eating food contaminated with bacteria or other microbes.


Reproductive structure; can be adapted for dispersal and survival in unfavorable conditions; found in bacteria, plants, algae, fungi, and some protozoa.

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Difficulty Level:

At Grade


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Mar 05, 2015
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