Pasteurization is a type of microbial control for food that uses heat but does not sterilize. Pasteurization kills pathogens while maintaining food quality. The process was developed by Louis Pasteur in the 1860s as a way to prevent beer and wine from spoiling. The process is commonly used to kill pathogens in milk, however the products may still spoil since they are not sterile.

Pasteurization

In $${}1862$$, Louis Pasteur conducted a series of experiments using flasks with long, twisted necks (swan-neck flasks) containing sterilized, boiled broth. The design allowed air to be exchanged but trapped airborne microorganisms in the bends of the neck, maintaining the sterility of the broth as long as the neck remained intact. If the neck was broken, microbes were introduced and contaminated the broth. This set of experiments irrefutably disproved the theory of spontaneous generation by showing that a 'life force' was not responsible for microbial growth, earning Pasteur the Alhumbert Prize.

Louis Pasteur's 1862 Swan-Neck Flask Experiment

The germ theory of disease states that diseases may result from microbial infection. Early proponents, such as Girolamo Fracastoro, suggested that seed-like spores could transfer between individuals, which laid early groundwork for this scientific theory.

Germ Theory of Disease

Louis Pasteur was a prominent French chemist who demonstrated that individual microbial strains possessed unique properties. While studying the causes of beer and wine spoilage in $${}1856$$, he discovered properties of fermentation by microorganisms and showed that it is caused by them. He demonstrated with his swan-neck flask experiments that airborne microbes, not spontaneous generation, were the cause of food spoilage. He suggested that if microbes were responsible for food spoilage and fermentation, they could also be responsible for causing infection, laying the foundation for the germ theory of disease. Furthermore, Pasteur invented pasteurization to kill microbes responsible for spoilage and developed vaccines for the treatment of diseases in both animals and humans, including rabies.

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Key scientists and their research led to our understandings about the field of Microbiology.

Notable Scientists in Microbiology

Pioneers in epidemiology include:
- John Snow
- Florence Nightingale
- Ignaz Semmelweis
- Joseph Lister
- Robert Koch
- Louis Pasteur

Pioneers in Epidemiology

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Edward Jenner coined the term "vaccination" after inoculating people with cowpox to prevent smallpox infections.

Edward Jenner

The "Golden Age of Microbiology" was a historical period spanning from $${}1857$$ to $${}1914$$ that spawned a host of new discoveries about the unseen world of microbes. During this time, famous microbiologists like Louis Pasteur and Robert Koch were especially active in advancing our understanding of microbiology.

Golden Age of Microbiology

Antonie van Leeuwenhoek, sometimes hailed as 'the Father of Microbiology,' was a Dutch cloth merchant who began his work in obscurity but became the first to develop innovative lens-making techniques for simple microscopes powerful enough to view microbes definitively. Using his simple microscope, which passed light through just one lens, he observed microorganisms as no one had before. His friend, the prominent physician Reinier de Graaf, helped bring attention to his powerful microscopes by writing to the Royal Society of London. From $${}1673$$ onward, van Leeuwenhoek regularly submitted letters to the society detailing his observations. In $${}1674$$, he described his groundbreaking observations of single-celled organisms. He described these organisms—which we now know were bacteria and protists observed in rain water—as 'animalcules' or 'wee little beasties.' His $${}1674$$ report initially produced controversy in the scientific community, but his claims were soon verified when the society sent a delegation to investigate his findings. He subsequently became a celebrated figure, at one point even entertaining a visit by the czar of Russia.

Antonie Van Leeuwenhoek

Louis Pasteur

Robert Koch was a German physician who became the first to definitively demonstrate the connection between a single, isolated microbe and a known human disease. Between 1867 and 1906, Koch and his colleagues determined the causative pathogens for numerous bacterial infections, successfully identifying the specific bacteria responsible for severe diseases such as anthrax, cholera, and tuberculosis.

Robert Koch

Spontaneous generation is one of the oldest theories regarding the origins of life, proposing that living organisms can arise from nonliving matter. This explanation can be traced back to the ancient Greeks and remained widely accepted throughout the Middle Ages.

Spontaneous Generation

Francesco Redi ($${}1626$$–$${}1697$$) was an Italian physician who performed one of the first experiments to refute the theory of spontaneous generation. In $${}1668$$, he hypothesized that preventing flies from contacting meat would prevent maggot formation. He placed meat in six containers: two open to the air, two covered with gauze, and two tightly sealed. Maggots developed only in the uncovered jars, leading Redi to conclude that maggots were the offspring of flies rather than a product of spontaneous generation.

Francesco Redi

In $${}1847$$, the Hungarian obstetrician Ignaz Semmelweis observed that patients giving birth in hospital wards staffed by physicians and medical students had a significantly higher mortality rate from puerperal fever ($${}10$$%–$${}20$$%) compared to those in wards staffed by midwives ($${}1$$%). He noticed that medical students performed autopsies and then conducted vaginal examinations on living patients without washing their hands in between. He suspected that the students were carrying disease from the autopsies to the patients, a suspicion supported when a physician friend died from a fatal wound infection caused by an autopsy scalpel, mirroring the illness of a deceased patient.

Ignaz Semmelweis

In $${}1867$$, British surgeon Joseph Lister sought to determine the causes of postsurgical infections, which were fatal for $${}50$$% of surgical patients on average. Familiar with the work of Semmelweis and Pasteur, he insisted on handwashing and extreme cleanliness during surgery. To further decrease infection rates, Lister began using carbolic acid (phenol) spray as a disinfectant and antiseptic during surgery. His extremely successful efforts to reduce postsurgical wound infections established his techniques as standard medical practice.

Joseph Lister

In $${}1966$$, scientist Thomas Brock ($${}1926$$–$${}2021$$) discovered that certain bacteria can live in boiling water. This discovery prompted scientists to investigate whether prokaryotes could also inhabit other extreme environments, such as deep-sea vents, high altitudes, volcanic areas, or other planets.

Thomas Brock's Discovery of Thermophilic Bacteria

In 1892, Russian botanist Dmitri Ivanovski discovered the source of tobacco mosaic disease (TMD) by passing infected tobacco plant extracts through a porcelain Chamberland filter. He observed that the disease-causing agent was not removed by the filter, leading him to conclude that TMD was caused by an extremely small bacterium or bacterial spore.

Dmitri Ivanovski's Discovery of Viruses

Wendell Stanley was the first scientist to crystallize the structure of the tobacco mosaic virus in 1935, discovering that it is composed of RNA and protein. In 1943, he isolated the Influenza B virus, contributing to the development of an influenza vaccine, and was awarded the Nobel Prize in 1946 for unlocking the mystery of the physical nature of viruses.

Wendell Stanley

In 1971, pathologist Theodor Diener at the Agriculture Research Service discovered an acellular, infectious particle that he named a viroid, meaning 'virus-like,' which was found to cause potato tuber spindle disease.

Discovery of Viroids

In 1982, medical doctor Stanley Prusiner discovered that scrapie—a fatal, degenerative disease in sheep—was caused by acellular, proteinaceous infectious particles called prions. Despite initial skepticism from scientists who believed all pathogens must contain DNA or RNA, his findings were eventually validated, earning him the 1997 Nobel Prize in Physiology or Medicine.

Stanley Prusiner

A British nurse considered  to be the founder of modern nursing; She carried out early epidemiological studies by keeping detailed records of soldiers' causes and deaths during the Crimean War and analyzed the data using histograms. Her data showed that most of the deaths could be attributed to preventable infectious diseases, leading to many hospital reforms in the British medical system.

(Photo credits in References)

Florence Nightingale

British physician John Snow is considered the 'Father of epidemiology' for his pioneering work in tracking cholera outbreaks in London. Beginning his studies in $${}1848$$, he later found the source of the $${}1854$$ Broad Street cholera epidemic. Snow demonstrated that cholera bacteria were transmitted via drinking water by tracing the outbreaks to specific water sources contaminated by sewage, such as a water pump on Broad Street fed by a common source spread. His research represents the first known epidemiological study and resulted in the first known public health response to an epidemic, which involved removing the Broad Street pump to contain the disease. Snow's work supported the germ theory of disease by hypothesizing that a microbe was the infectious agent spreading through fecal-oral transmission. Along with the work of Ignaz Semmelweis, Snow's findings clearly refuted the prevailing miasma theory of the day, showing that disease is not only transmitted through the air but also through contaminated items.

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