Chapter 2

Microbiology: The Young Science

In This Chapter

Remembering a time before microbiology

Discovering microorganisms step-by-step

Looking forward

Compared with other more ancient fields of science, microbiology is a relative baby. Physics began in ancient times, mathematics even earlier, but the knowledge of tiny living things, their biology, and their impact on human lives has only been around since the late 19th century. Until about the 1880s, people still believed that life could form out of thin air and that sickness was caused by sins or bad odors.

As with other fields in science, there are two aspects to microbiology research: basic and applied. Basic microbiology is about discovering the fundamental rules governing the microbial world and studying all the variety of microbial life and microbial systems. Applied microbiology is more about solving a problem and involves using microbes and their genes or proteins for practical purposes such as in industry and medicine.

In this chapter, we introduce the key concepts and experiments that gave rise to the discovery of microbes and their importance in disease. This chapter also highlights the many different areas of study within microbiology and some advances and challenges in the prevention and treatment of infectious diseases.

Before Microbiology: Misconceptions and Superstitions

Medical practices in ancient times were all heavily tinged with supernatural beliefs. Ancient Egypt was ahead of its time in terms of medicine, with physicians performing surgery and treating a wide variety of conditions. Medicine in India was also quite advanced. Ancient Greek physicians were concerned with balancing the body’s humors (the four distinct body fluids that they believed were responsible for health when in balance, or disease when out of balance), and medicine in medieval Europe was based on this tradition. None, however, had knowledge of the microbial causes of disease.

Opinions about why diseases afflicted people differed between cultures and parts of society, and the treatments differed as well. Diseases were thought to be caused by

• Bad smells, treated by removing or masking the offending odor
• An imbalance in the humors of the body, treated with bleeding, sweating, and vomiting
• Sins of the soul, treated with prayer and rituals

Although the concept of contagion was known, it wasn’t attributed to tiny living creatures but to bad odors or spirits, such as the devil. So, simple measures, such as removing sources of infection or washing hands or surgical equipment, were simply not done.

Discovering Microorganisms

Before microorganisms were discovered, life was not known to arise uniquely from living cells; instead, it was thought to spring spontaneously from mud and lakes or anywhere with sufficient nutrients in a process called spontaneous generation. This concept was so compelling that it persisted until late into the 19th century.

Robert Hooke, a 17th-century English scientist, was the first to use a lens to observe the smallest unit of tissues he called “cells.” Soon after, the Dutch amateur biologist Anton van Leeuwenhoek observed what he called “animalcules” with the use of his homemade microscopes.

When microorganisms were known to exist, most scientists believed that such simple life forms could surely arise through spontaneous generation. So, when they heated a container, placed a nutrient broth (a mixture of nutrients that supported growth of microorganisms in these early experiments) in the container and then sealed it, and no microorganisms appeared, they believed it had to be due to the absence of either air or the vital force (whatever that was!) necessary to make life.

Debunking the myth of spontaneous generation

The concept of spontaneous generation was finally put to rest by the French chemist Louis Pasteur in an inspired set of experiments involving a goose-necked flask (see Figure 2-1). When he boiled broth in a flask with a straight neck and left it exposed to air, organisms grew. When he did this with his goose-necked flask, nothing grew. The S-shape of this second flask trapped dust particles from the air, preventing them from reaching the broth. By showing that he could allow air to get into the flask but not the particles in the air, Pasteur proved that it was the organisms in the dust that were growing in the broth. This is the principle behind the Petri dish used to grow bacteria on solid growth medium (made by adding a gelling material to the broth), which allows air but not small particles to reach the surface of the growth medium.

The idea that invisible microorganisms are the cause of disease is called germ theory. This was another of the important contributions of Pasteur to microbiology. It emerged not only from his experiments disproving spontaneous generation but also from his search for the infectious organism (typhoid) that caused the deaths of three of his daughters.

Around the same time that Pasteur was doing his experiments, a doctor named Robert Koch was working on finding the causes of some very nasty animal diseases (first anthrax, and then tuberculosis). He devised a strict set of guidelines — named Koch’s postulates — that are still used to this day to definitively prove that a microorganism causes a particular disease. Koch’s four postulates are

• The organism causing the disease can be found in sick individuals but not in healthy ones.
• The organism can be isolated and grown in pure culture.
• The organism must cause the disease when it is introduced into a healthy animal.
• The organism must be recovered from the infected animal and shown to be the same as the organism that was introduced.

Improving medicine, from surgery to antibiotics and more

Once scientists knew that microbes caused disease, it was only a matter of time before medical practices improved dramatically. Surgery used to be as dangerous as not doing anything at all, but once aseptic (sterile) technique was introduced, recovery rates improved dramatically. Hand washing and quarantine of infected patients reduced the spread of disease and made hospitals into a place to get treatment instead of a place to die.

Vaccination was discovered before germ theory, but it wasn’t fully understood until the time of Pasteur. In the late 18th century, milkmaids who contracted the nonlethal cowpox sickness from the cows they were milking were spared in deadly smallpox outbreaks that ravaged England periodically. The physician Edward Jenner used pus from cowpox scabs to vaccinate people against smallpox. Years later, Pasteur realized that the reason this worked was that the cowpox virus was similar enough to the smallpox virus to kickstart an immune response that would provide a person with long-term protection, or immunity.

Antibiotics were discovered completely by accident in the 1920s, when a solid culture in a Petri dish (called a plate) of bacteria was left to sit around longer than usual. As will happen with any food source left sitting around, it became moldy, growing a patch of fuzzy fungus. The colonies in the area around the fungal colony were smaller in size and seemed to be growing poorly compared to the bacteria on the rest of the plate, as shown in Figure 2-2.

The compound found to be responsible for this antibacterial action was named penicillin. The first antibiotic, penicillin was later used to treat people suffering from a variety of bacterial infections and to prevent bacterial infection in burn victims, among many other applications.

After bacteria were discovered, the field of molecular biology made great strides in understanding the genetic code, how DNA is regulated, and how RNA is translated into proteins. Until this point, research was focused mainly on plant and animal cells, which are much more complex than bacterial cells. When researchers switched to studying these processes in bacteria, many of the secrets of genes and enzymes started to reveal themselves.

Looking at microbiology outside the human body

Two important microbiologists helped shape our understanding of the microbial world outside the human body and gave rise...