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Bacterial Diseases

Bacterial Diseases

Bacteria get a bad reputation for causing disease when, in reality, very few species of bacteria infect humans. The ones that do, however, are the ones most often written about in magazines and newspapers. These bacteria inhabit the human body because of the constant source of nourishment, moist environment, relatively stable pH and body temperature, and extensive surface area.


Physician and bacteriologist who isolated a strain of the bacterium that causes diphtheria, from which she made an antitoxin that could be used to treat the disease. She also discovered a way to diagnose rabies in a few minutes instead of a few days, thus saving many more lives.

Contamination with bacteria from the environment can lead to colonization, taking up residence on or in the human body. The mixed collection of bacteria that are adapted to the body and reside in it for extended periods of time are called normal flora. Some bacteria inhabit the body only as transients, soon destroyed by human (host) defense mechanisms or removed by cleaning. Bacteria that evade host defenses and cause infection are described as virulent. Under certain circumstances, such as an imbalance in normal flora or lowered host resistance, even normal flora can cause infection.

Infection may proceed to disease if host defenses do not arrest the infection before tissue damage occurs. Bacterial disease can have several outcomes. The immune system may arrest the infection and stop progression of the disease. In other cases, the body may be unable to repair damaged tissues and permanent dysfunction or even death may result. For this reason, treatments are designed to stop the infection before permanent damage has occurred.

KOCH, ROBERT (18431910)

German physician who discovered the three bacteria that cause the deadly diseases tuberculosis, cholera, and anthrax, and who won the 1905 Nobel Prize in medicine. His most enduring work was a set of guidelines, called Koch's postulates, for telling which pathogens (bacteria or viruses) cause which diseases.

Most bacterial diseases are treated with antibiotics to kill the organisms. In recent years, more and more bacteria have become resistant to the available antibiotics. This has forced the scientific community to examine the use of antibacterial agents in soaps and cleansers, the use of antibiotics in animal feeds, and the inappropriate prescription of antibiotics. Patients who terminate the treatment prematurely because they feel better, even though the infection is not yet eliminated, compound the problem of antibiotic resistance. All of these situations lead to the killing off of susceptible bacteria while leaving the resistant ones to multiply. The best "medicine" is still prevention of infection.

see also Disease; Eubacteria

Jackie Butler


Berkow, Robert, et al. The Merck Manual of Diagnosis and Therapy, 17th ed. Rahway, NJ: Merck & Co., 1999.

Levy, Stuart B. "The Challenge of Antibiotic Resistance." Scientific American (March 1998). <>.

Murray, Patrick R., et al. Medical Microbiology, 3rd ed. St. Louis: Mosby-Year Book, 1998.

Staley, James T., et al. Bergey's Manual of Systematic Bacteriology, 4 vols. Philadelphia, PA: Lippincott, Williams & Wilkins, 19841989.

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Bacterial Infections

Bacterial Infections

How are Bacteria Different?

How are Bacterial Infections Diagnosed and Treated?

How are Bacterial Infections Prevented?

How Do Bacteria Become Drug Resistant?


Bacterial infections are illnesses that occur when harmful forms of bacteria multiply inside the body. They range from mild to severe. Although they include such deadly diseases as plague, tuberculosis, and cholera, these and many other bacterial infections can be prevented by good sanitation or cured by antibiotics.


for searching the Internet and other reference sources


Antibiotic resistance


Drug resistance


Bacteria are everywhere: in soil, in water, in air, and in the bodies of every person and animal. These microorganisms* are among the most numerous forms of life on Earth.

* microorganisms
are living organisms that can only be seen using a microscope. Examples of microorganisms are bacteria, fungi, and viruses.

Most bacteria are either harmless, or helpful, or even essential to life. Bacteria break down (decompose) dead plants and animals. This allows chemical elements like carbon to return to the earth to be used again. In addition, some bacteria help plants get nitrogen. Without them, plants could not grow. In the human body, bacteria help keep the digestive tract working properly.

Like viruses, however, bacteria can cause hundreds of illnesses. Some bacterial infections are common in childhood, such as strep throat and ear infections. Others cause major diseases, such as tuberculosis, plague, syphilis, and cholera. The infection may be localized (limited to a small area), as when a surgical wound gets infected with a bacterium called Staphylococcus (staf-i-lo-KOK-us). It may involve an internal organ, as in bacterial pneumonia (infection of the lungs) or bacterial meningitis (infection of the membrane covering the brain and spinal cord).

Some bacteria, such as pneumococcus (noo-mo-KOK-us), which is also called Streptococcus pneumoniae, almost always cause illness if they get into the body. Others, such as Escherichia coli, usually called by the short form E. coli, often are present without doing harm. If the immune system is weakened, however, these bacteria can grow out of control and start doing damage. Such illnesses are called opportunistic infections. They have become more common in recent years, in part because AIDS, organ transplants, and other medical treatments have left more people living with weakened immune systems.

Food Poisoning

Food poisoning is often the result of bacterial contamination. Important precautions for preventing food poisoning include:

  • Avoiding raw or undercooked meat, poultry, seafood, and eggs.
  • Avoiding non-pasteurized dairy products.
  • Throwing out food items that are old or have an off smell.
  • Keeping foods cold until ready to serve.
  • Storing and cooking foods properly.
  • Washing knives, cutting boards, cooking utensils, and food preparation areas after every use.
  • Washing hands before preparing food, before eating, and after using the bathroom.

How are Bacteria Different?

Unlike other living cells, bacteria do not have a membrane enclosing their nucleus, the part of the cell containing DNA, or genetic matter. Unlike viruses, most bacteria are complete cells that can reproduce on their own without having to invade a plant or animal cell. Some bacteria, however, do need to live inside another cell just as viruses do.

HOW do bacterial infections spread?

Different bacteria spread in different ways. Examples include:

  • through contaminated water (cholera and typhoid fever)
  • through contaminated food (botulism, E. coli food poisoning, salmonella food poisoning)
  • through sexual contact (syphilis, gonorrhea, chlamydia)
  • through the air, when infected people sneeze or cough (tuberculosis)
  • through contact with animals (anthrax, cat scratch disease)
  • through touching infected people (strep throat)
  • from one part of the body, where they are harmless, to another part, where they cause illness (as when E. coli spread from the intestines to the urinary tract).

How do bacteria cause illness?

Bacteria can cause illness in several ways. Some destroy tissue directly. Some become so numerous that the body cannot work normally. And some produce toxins (poisons) that kill cells. Exotoxins are poisons released by live bacteria. Endotoxins are poisons released when the bacteria die.

How are Bacterial Infections Diagnosed and Treated?

Symptoms of bacterial infections vary widely but often include fever.


Doctors may test the blood, sputum, or urine for evidence of harmful bacteria. If a lung infection is suspected, the doctor may take a chest x-ray or do a biopsy, taking cells from an infected area to be examined. If meningitis is suspected, the doctor may do a spinal tap, using a needle to extract a sample of the spinal fluid surrounding the spinal cord for testing.


Most bacterial infections can be cured by antibiotic drugs, which were one of the great medical success stories of the twentieth century. These drugs either kill the bacteria or prevent them from reproducing. Penicillin, the first antibiotic, is still used to treat some infections. Other widely used antibiotics include amoxicillin, bacitracin, erythromycin, cephalosporins, fluroquinolones, and tetracycline. Sometimes antitoxins are also given to counter the effects of bacterial toxins, as in the case of tetanus or botulism.

Flesh-Eating Bacteria

A virulent strain of Streptococcus A bacteria caused illness in 117 people in Texas between December 1997 and March 1998. Of those 117 infections, 26 (17 adults and 9 children) resulted in deaths. Described in media coverage as flesh-eating bacteria, these pathogens caused their damage through a process called hemolysis (he-MOL-y-sis), which causes red blood cells to disintegrate. The Texas outbreak was short lived, and experts still do not know how it started.

How are Bacterial Infections Prevented?

Young children commonly get shots of vaccine to prevent diphtheria, whooping cough, tetanus, and Hemophilus influenza B, all bacterial infections. In addition, vaccines are available to help prevent cholera, meningococcal and pneumococcal infections, plague, and typhoid fever.

For many bacterial infections, good living conditions are the best prevention. That means clean water supplies, sanitary disposal of human waste, well-ventilated housing that is not overcrowded, and prompt medical treatment for people who do get sick.

Other steps include:

  • Washing hands (before handling food; after using the toilet; after touching animals; after having contact with infected people).
  • Washing fruits and vegetables before eating.
  • Cooking meat thoroughly.
  • Abstaining from sexual contact, or using condoms during sexual activity.

How Do Bacteria Become Drug Resistant?

Each kind of bacteria can be killed by certain antibiotics and each kind is naturally resistant to others. But in recent years, some bacteria have developed resistance to antibiotics that used to kill them. This is one of the big problems in controlling infectious diseases.

How does resistance occur?

In some cases, it occurs by chance. As bacteria reproduce, mutations (variations) in their genes occur all the time. One of these mutations may happen, by chance, to make one bacterium in a persons body less vulnerable to a drug. This bacterium multiples along with other bacteria. While other bacteria are killed off by the drug, the mutatedor resistantbacterium thrives, and eventually spreads from person to person.

Why does resistance occur more often now?

Humans can make drug resistance far more likely to develop than it would simply by chance. They do this when they use antibiotics that are not needed or when they do need antibiotics but stop taking them too soon.

Here is how those practices can increase resistance: Let us say that a man has a bacterial infection. He takes an antibiotic, feels better, and stops taking the drug in five days, even though the doctor said to take it for 10 days. Inside the mans body, the drug may have killed, say, 80 percent of the bacteria. That was enough to make the man feel better. But the bacteria still alive are the 20 percent that were toughest, the ones best able to survive the drug. If the man had kept taking the antibiotic, the toughest bacteria might have been killed on Day 8, 9, or 10. But now, left alone, they start to multiply. Soon the person feels sick again. But this time, all the bacteria in his body are the tougher kind. A scientist would say the persons behavior selected the most resistant bacteria for survival.

A similar process occurs when doctors prescribe antibiotics that are not needed. Let us say that a girl has a cough and fever. The doctor prescribes antibiotics on the chance that the girl has a bacterial infection. But she actually has a virus, and viruses cannot be treated with antibiotics. The girls immune system, her natural defense system, fights off the virus as it would have without the drug. Meanwhile, the antibiotic kills off some bacteria that usually live harmlessly in the girls throat. The bacteria in her throat that survive are those that are better at resisting the antibiotic. Later, if those bacteria get into her ears, her lungs, or some other part of her body where they can cause illness, the antibiotic may not work as well against them.

If events like these happen countless times, in countless people, eventually strains of bacteria may arise that partially or completely resist a drug that used to kill them.

See also



Cat Scratch Disease


Chlamydial Infections



Food Poisoning


Legionnaires Disease


Lyme Disease



Peptic Ulcer



Rheumatic Fever

Rocky Mountain Spotted Fever


Strep Throat


Toxic Shock Syndrome

Typhoid Fever





U.S. Centers for Disease Control and Prevention (CDC). CDC posts a fact sheet called Bacterial Diseases at its website.

U.S. Food and Drug Administration (FDA). The FDA posts a Bad Bug Book at its website that offers fact sheets about many different pathogenic bacteria.

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