Manipulating Biology: Costs, Benefits and Controversies

The Germ Theory of Disease

While today we take for granted the idea that microscopic organisms can cause illness and disease, this idea was revolutionary and was not widely accepted until much later than the concept of vaccination. Jenner was able to empirically demonstrate that smallpox vaccination worked but did not offer a comprehensive view about the underlying cause of the disease. That is because germ theory was not yet widely accepted. The predominant theory was spontaneous generation.  

Even as far back as 1658, scientists were able to view microorganisms under a microscope, but did not make the link that some microbes are disease agents. The common belief was that living organisms could arise from nonliving things. Decomposition, fermentation and the like were considered to spontaneously arise. This would later be disproven by Louis Pasteur.

Louis Pasteur (1822 – 1895)

Louis Pasteur was a French scientist who conducted research on microbiology in the 19^th century, and the process of pasteurization was named for him. The experimental evidence debunking the theory of spontaneous generation came from Louis Pasteur. In order to prove that life could not originate from nonliving matter and to prove his germ theory once and for all, Pasteur set out to devise an experiment to test germ theory.

Figure 1: Louis Pasteur’s experiment illustrates that spoilage does not spontaneously generate.

Creative Commons 4.0. Author: Kgerow16.

Pasteur’s experiment started with a preparation of a nutrient broth similar to a soup. He placed equal amounts into long necked flasks, one with a straight neck and one curved. Both of the flasks were boiled to sterilize any living matter in the broth. They were allowed to sit for several weeks afterward at room temperature. He noted that the broth exposed directly to the air was cloudy and had microorganisms living in it, but the broth where germs could not land in the flask was still clear.¹³

The idea that microorganisms are responsible for decomposition and contamination is taken for granted today. The discovery that life does not spontaneously generate but comes from other life has been added to the pantheon of scientific knowledge alongside evolution. ¹⁴

But the full medical implications for germ theory would not come close to its full potential and use until the advent of Joseph Lister’s surgical techniques.

Joseph Lister (1827 – 1912)

Lister is well known for his practices regarding antiseptic surgical techniques in a time when even simple practices like handwashing were unheard of in a medical context. He used carbolic acid spray on surgical sites and insisted on clean instruments, whereas other surgeons wore clothing with blood splatters from one patient while working on other patients.

Convincing fellow doctors of the threat from microorganisms got easier after Lister operated on Queen Victoria to drain an abscess, using his techniques to help save her life. He would later be knighted for his efforts in improving surgical outcomes.¹⁵

What inspired Lister’s breakthrough and belief in microorganisms causing disease? Simply put, he had been encouraged to read over Louis Pasteur’s papers, Researches sur la putrefaction (Research on Putrifaction) and made the intellectual leap that the same thing that causes food spoilage could be affecting injured people, especially those with compound fractures of bones that broke the skin and were exposed to the air.¹⁶

His ideas that invisible microorganisms were responsible for disease was generally supported by the research of Robert Koch, who worked to show which germs caused which diseases.

Robert Koch (1843 – 1910) and his Postulates

Robert Koch’s first major breakthrough came from working with anthrax (a bacterial disease) and farm animals. Koch started by confirming the work of prior scientists. He inoculated mice with material from the spleens of cattle who had died of anthrax as well as another set of mice that were inoculated with material from the spleens of healthy animals. The mice that received the spleen material with the anthrax bacilli died.¹⁷ This was Koch’s first step in confirming that there was a link between a specific disease and a specific microorganism.

Koch continued his work by growing pure bacilli samples in the laboratory on newly invented petri dishes and he developed new ways of staining bacteria to make them easier to observe under the microscope.¹⁸ Koch’s additional work went on to isolate the disease-causing agent for Tuberculosis.¹⁹

To understand how to isolate and prove that certain diseases were caused by a specific microorganism, Koch established four basic postulates:

Figure 2: Koch’s postulates which are designed to establish causal relationships between disease and microorganisms. Creative Commons 3.0. Author: Mike Jones.

1. A specific microorganism is always associated with a given disease.
2. The microorganism can be isolated from the diseased animal and grown in pure culture in the laboratory.
3. The cultured microbe will cause disease when transferred to a healthy animal.
4. The same type of microorganism can be isolated from the newly infected animal.²⁰

The application of Koch’s postulates is not universal. Sometimes organisms cannot actually be grown in a culture separately from a living host, so some disease causing microbes would fail to meet all of Koch’s postulates. What they do demonstrate is the importance of establishing casual relationships rather than simple correlative relationships that can often be mistaken for causal, as we will later see with the relationship between vaccination and autism.

Why is it important to understand the history of germ theory to understand and teach vaccination? While Jenner relied on science to the extent that he performed epidemiological research, formulated a hypothesis, and tested it, he did so without fully understanding the science of disease or the causes of smallpox and cowpox (different infectious agents).

By modern standards, Jenner was putting people at risk in his experiments. Today we know that in order for vaccines to be effective, they rely on the proven relationship between disease causing viruses and bacteria and the actual disease they cause. Perhaps this is why it took almost 100 years and additional work before other vaccines were created. So, how do vaccines work?