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Bacteria And Disease

The medical community did not accept the concept that bacteria can cause disease until well into the nineteenth century. Joseph Lister, an English surgeon, applied the so-called "germ theory" to medical practice in the 1860s. Lister soaked surgical dressing in carbolic acid (phenol), which reduced the rate of post-surgical infections so dramatically that the practice spread.

In 1876, the German physician Robert Koch identified Bacillus anthracis as the cause of anthrax, and in so doing, developed a series of laboratory procedures for proving that a specific organism can cause a specific disease. These procedures, called Koch's postulates, are still generally valid. Briefly, they state that, to prove an organism causes a specific disease, the investigator must:

  1. Find the same pathogenic microorganism in every case of the disease.
  2. Isolate the pathogen from the diseased patient or experimental animal and grow it in pure culture.
  3. Demonstrate that the pathogen from the pure culture causes the disease when it is injected into a healthy laboratory animal.
  4. Isolate the pathogen from the inoculated animal and demonstrate that it is the original organism injected into the animal.

The ability to isolate, study, and identify bacteria has greatly enhanced the understanding of their diseasecausing role in humans and animals, and the subsequent development of treatments. Part of that understanding derives from the realization that since bacteria are ubiquitous and are found in large numbers in and on humans, they can cause a wide variety of diseases.

The skin and the nervous, cardiovascular, respiratory, digestive and genitourinary systems are common sites of bacterial infections, as are the eyes and ears.

The skin is the body's first line of defense against infection by bacteria and other microorganisms, although it supports enormous numbers of bacteria itself, especially Staphylococcus and Streptococcus species. Sometimes these bacteria are only dangerous if they enter a break in the skin or invade a wound, for example, the potentially fatal staphylococcal toxic shock syndrome. Among other common bacterial skin ailments are acne, caused by Propionibacterium acnes and superficial infection of the outer ear canal, caused by Pseudomonas aeruginosa.

Among the neurological diseases are meningitis, an inflammation of the brain's membranes caused by Neisseria meningitidis and Hemophilus influenzae.

Many medically important bacteria produce toxins, poisonous substances that have effects in specific areas of the body. Exotoxins are proteins produced during bacterial growth and metabolism and released into the environment. Most of these toxin-producing bacteria are gram positive.

Among the gram positive toxin-producing bacteria are Clostridium tetani, which causes tetanus, an often fatal paralytic disease of muscles; Clostridium botulinum, which causes botulism, a form of potentially lethal food poisoning; and Staphylococcus aureus, which also causes a form of food poisoning (gastroenteritis).

Most gram negative bacteria (for example, Salmonella typhi, the cause of typhoid fever) produce endotoxins, toxins that are part of the bacterial cell wall.

As the role of bacteria in causing disease became understood, entire industries developed that addressed the public health issues of these diseases.

As far back as 1810, the French confectioner Nicholas Appert proved that food stored in glass bottles and heated to high temperatures could be stored for long periods of time without spoiling. Appert developed tables that instructed how long such containers should be boiled, depending upon the type of food and size of the container. Today, the food preservation industry includes not only canning, but also freezing and freeze-drying. An important benefit to food preservation is the ability to destroy potentially lethal contamination by Clostridium botulinum spores.

Even as concepts of prevention of bacterial diseases were being developed, scientists were looking for specific treatments. Early in the twentieth century, the German medical researcher Paul Ehrlich theorized about producing a "magic bullet" that would destroy pathogenic organisms without harming the host.

In 1928, the discovery by Scottish bacteriologist Alexander Fleming that the mold Penicillium notatum inhibited growth of Staphylococcus aureus ushered in the age of antibiotics. Subsequently, English scientists Howard Florey and Ernst Chain, working at Oxford University in England, demonstrated the usefulness of penicillin, the anti-bacterial substance isolated from P. notatum in halting growth of this bacterium. This inhibitory effect of penicillin on bacteria is an example of antibiosis, and from this term is derived the word antibiotic, which refers to a substance produced by microorganisms that inhibits other microorganisms.

Beginning in the 1930s, the development of synthetic anti-bacterial compounds called sulfa drugs further stimulated the field of anti-bacterial drug research. The many different anti-bacterial drugs available today work in a variety of ways, such as the inhibition of synthesis of cell walls, of proteins, or of DNA or RNA.

Today, medical science and the multi-billion dollar pharmaceutical industry are facing the problem of bacterial resistance to drugs, even as genetically engineered bacteria are being used to produce important medications for humans.

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