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.

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.

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


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Staley, James T., et al. Bergey's Manual of Systematic Bacteriology, 4 vols. Philadelphia, PA: Lippincott, Williams & Wilkins, 1984–1989.


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.

KOCH, ROBERT (1843–1910)

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.

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