PREFACE
For many of us, the word “microbe” still conjures a negative image, one of sickness, infection, or contamination. In general, we do not wonder “Where does this microbe come from?” except in case of an epidemic. We simply observe that its presence is inopportune and is dismantling a preestablished order, an equilibrium: this well-being that is named “health.”
We now know, however, that good health depends on the presence of millions of beneficial microbes and microorganisms. These live on our skin and in different places in our bodies, such as the intestine, the mouth, and the nose, or they participate in various processes, such as the making of cheese, yogurt, and other foods, or water treatment and environment decontamination. They play a key role in maintaining the stability of our environment and the biodiversity of the flora and fauna of our planet.
Thanks to the studies of Louis Pasteur and Robert Koch at the end of the 19th century, it is well established that microbes do not spontaneously generate, that each microbe is born from another microbe, and that the smallest living organisms capable of autonomous life are called bacteria (from the Greekbakteria, meaning a stick or rod, named for the rod-like shape of the first observed bacteria). These bacteria, observable with simple microscopes, are single-celled organisms that can generate thousands of similar unicellular daughter cells.
Louis Pasteur and Robert Koch importantly discovered that bacteria were responsible for numerous diseases that have devastated humanity for thousands of years, such as the plague, cholera, and tuberculosis. Their studies paved the way for powerful methods of diagnosis of, and treatment for, bacterial infections, and for the development of vaccines, some of which are still being used today. Pasteur and Koch also introduced the concept of the study of bacteria in general, whatever their nature—i.e., either pathogenic, illness-generating bacteria or nonpathogenic bacteria that carry out other functions. In fact, the discoveries of Pasteur, Koch, and their collaborators were so revolutionary and so important that by the early 20th century they triggered an immense interest, first among medical doctors and then among biologists of all sorts attracted to this new discipline: microbiology, the study of various microorganisms invisible to the naked eye, and more specifically, bacteriology, the study of bacteria.
During this flourishing period and the entire century that has followed, the field has advanced by leaps and bounds in many directions. At first, shortly after Pasteur and Koch, microbiology developed rather slowly, with the meticulous identification of all kinds of bacteria, the establishment of various collections, and diverse classifications and precise descriptions. Then things really sped up. In the early 1950s, the discovery of DNA as the basis of the genetic material of all living organisms, combined with the previous research on bacteria, quickly led to the development of concepts that applied, as Nobel laureate Jacques Monod put it, to the bacterium as much as to the elephant. These concepts included DNA replication, DNA transcription, protein translation, and protein synthesis. This in turn led to the development of molecular biology and genetic engineering: the art of manipulating genes and species.
By the end of the 20th century, technologies in DNA sequencing—the determination of the structure of genes and, soon, of complete bacterial genomes—sparked a totally unexpected acceleration in the study of bacteria, both pathogenic and not. Our understanding of infectious diseases was completely redefined by these approaches that, in association with cellular biology techniques such as imaging, started to shed light on the multiple mechanisms used by microorganisms to establish infection by interacting in various ways with the infected host and by harnessing many of the host’s essential functions and fundamental mechanisms.
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