only on Petri dishes, that is a bit of a misconception. Nature frequently provides its own colonies. Sometimes you can see whole populations of microbes “bloom.” Purple sulfur bacteria create a rather pretty colony, for example. Those of you who are skiers have probably seen “water melon snow” created by cold-tolerant algae and cyanobacteria that grow on snow and ice during alpine and polar summers. And, of course, in the world of rot and ruin, microbes are frequently visible. They make ugly colonies when they spoil fruit, vegetables, and other food stuffs. Microbes also have been known by the good things they do, such as their uses in bread making and fermentation, which go back to the early stages of civilization. Yeast is the microbe used in making bread; it provides the leavening. Similarly, yeasts are essential for the fermentation of wine and beer. People harnessed yeast metabolism for centuries without knowing that they were working with a microbe.
Microbes are best known for the diseases they cause. Pathogen is the general name for an organism that causes a disease, and is used to describe all microbes able to cause disease in animals and/or plants. Infectious diseases are those that spread from one person to another. An infectious disease can be more formally defined as a clinically evident disease resulting from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular parasites, and the aberrant proteins known as prions.
When we consider microbiology, we often think about the traditional scourges. One is leprosy, which has many references in the Bible and other classical literature. The causative bacterium of leprosy, also known as Hansen’s disease, is Mycobacterium leprae. A second notorious infectious disease of antiquity is plague caused by Yersinia pestis. The “Black Death,” as it was known, killed a third of Europe’s population during the 14th century. It got this name from the black skin splotches it caused on affected people. Swollen lymph glands, or buboes, are the basis of the name “bubonic plague.” The word plague, which should be used narrowly to describe just that one disease, often has come to be used as a general term for any devastating epidemic disease. Tuberculosis, for example, is sometime called the white plague.
In addition, many viral diseases have been known since ancient times. These include chicken pox, influenza, mumps, polio, rabies, and yellow fever. Most of these diseases are still very much with us. On the other hand, smallpox, in one of the great triumphs of public health and microbiology, has been eradicated. Young people are no longer vaccinated. A corollary of the eradication of small pox: If you want a good bioterrorism weapon, you do not have to do any genetic engineering—just unleash smallpox again.
Professional Societies, Journals, and Culture Collections
What about the professional societies organized by microbiologists? Microbiologists started organizing themselves into professional groups right after the research of Koch and Pasteur changed the face of medicine and public health. The American Society for Microbiology (ASM), the society that I know best, is not only the world’s oldest microbiological society but is also one of the world’s oldest biological societies. It was founded in 1899, well over a hundred years ago. It was initially named the Society for American Bacteriologists, and for quite a while, even though it had members who worked on viruses and fungi, its members referred to what they did as bacteriology. The Society name was changed from the American Society for