Bacteriology

The microscope is one of the most important tools used in studying bacteria. Dyeing or staining bacterial specimens or cultures was introduced in 1871 by the German pathologist Karl Weigert and has greatly helped the bacteriologist in identifying and observing bacteria under the microscope. A bacterial specimen is first placed on a glass slide. After the specimen has dried, it is stained to render the organism easier to observe. Stains also stimulate reactions in certain bacteria. For example, the tuberculosis bacillus can be recognized only on the basis of its reaction to certain stains (see Gram's Stain). Bacteriologists have been greatly aided by the electron microscope, which has far greater magnification powers than ordinary microscopes.

In recent years, bacteriology has been greatly expanded from its concentration on bacterial disease. The discovery that bacteria fix nitrogen in the root nodules of leguminous plants (see Nitrogen Fixation) has led to attempts to inoculate the roots of other plant strains and thereby increase soil fertility and the productivity of food crops. Some bacteria are able to digest petroleum and other hydrocarbons; others absorb phosphorus. These bacteria are being intensively investigated as possible aids in cleaning up oil spills and removing phosphorus from sewage sludge (Bioremediation). Other bacteria may be more efficient than yeast at producing alcohol and are being explored in the search for new energy sources. Escherichia coli, a normal inhabitant of the human intestinal tract, is the most thoroughly studied of all organisms. Studies of the mechanisms of genetic exchange and the biology of plasmids and bacteriophages of E. coli have been crucial in understanding many aspects of DNA replication and the expression of genetic material. These studies have led to the ability to insert DNA from unrelated organisms into E. coli plasmids and bacteriophages and to have that DNA replicated by the bacteria, with the genetic information it contains expressed by the bacteria. It is thus possible for bacteria to become living factories for scarce biological products such as human insulin, interferon, and growth hormone. See Genetic Engineering.

Advances in research using the tools of molecular genetics have also led to greater understanding of the mechanisms of disease-causing organisms. Since 1995 the complete sequences of the genome (genetic blueprint) of several important organisms that cause human disease have been determined. Understanding the genetic makeup of these organisms, including Mycobacterium tuberculosis, the bacterium that causes tuberculosis; and Haemophilus influenzae, which is linked to meningitis and responsible for recurring childhood ear infections, will likely lead to the development of new drugs and vaccines against the microbes. Since these organisms are able to mutate and become resistant to antibiotics, research is ongoing to attempt to control the virulence of these organisms once they have become resistant.