The bacterium Escherichia coli (E. coli) is one of the most extensively studied organisms in biology, serving as a model for molecular genetics and biotechnology research. While often associated with foodborne illness, most strains are harmless inhabitants of the intestinal tract in warm-blooded animals. Understanding the history of E. coli provides insight into how scientific focus shifts from identifying normal flora to isolating disease agents. The initial discovery and subsequent reclassification of this common intestinal microbe form a chapter in the history of microbiology.
The Context and the Discoverer
The bacterium was discovered in 1885 by Theodor Escherich, a German-Austrian physician who was a pioneer in pediatrics and bacteriology. This period was marked by the rapid advancement of the “Golden Age of Bacteriology,” with scientists like Robert Koch and Louis Pasteur establishing the germ theory of disease. Escherich was working at a time when physicians began looking closely at the specific microbes associated with health and sickness.
Escherich’s primary research focus was on the gut flora of infants, specifically investigating which bacteria were present in the feces of healthy babies. He utilized new laboratory methods, including Hans Christian Gram’s recently developed staining technique, to isolate and study bacteria from infant stool samples. His intent was to understand the digestive process and identify organisms that might aid in normal development.
His work culminated in the 1886 publication, Die Darmbakterien des Säuglings (The Intestinal Bacteria of the Infant), which formally described the organism. Escherich’s detailed descriptions of the rod-shaped, gram-negative bacterium were foundational for recognizing its omnipresence in the human colon. His work marked a significant step in the study of fecal enterobacteria, providing a baseline for what constituted a normal gut environment.
Initial Naming and Classification
When Escherich first identified the organism, he named it Bacterium coli commune. The term Bacterium was a common genus designation at the time, while coli referred to the colon, the site where the organism was predominantly found. The species name commune emphasized its communal nature, reflecting its perceived role as a common, non-pathogenic resident of the gut.
For decades, the microbe was considered benign or beneficial, helping prevent colonization of the intestine by more harmful bacteria and contributed to the production of vitamins, such as vitamin K. The name was later revised to honor its discoverer. In 1919, the genus was formally renamed Escherichia, leading to the current designation Escherichia coli. This renaming was not officially endorsed by the scientific community until 1958, but it solidified the legacy of its discoverer.
Shift in Scientific Perspective
The initial classification of E. coli as a harmless communal bacterium stood for many years, but scientific understanding began to shift in the early 20th century. Researchers began to isolate specific strains from patients suffering from severe diarrhea, particularly infants, suggesting that not all E. coli were benign. This indicated the species was far more diverse than originally thought.
The major change came with the discovery that certain E. coli strains had acquired virulence genes, allowing them to cause disease. These genetic elements can be transferred through mechanisms like horizontal gene transfer, turning a commensal organism into a pathogen. The species is now categorized into various pathotypes, such as Enteropathogenic E. coli (EPEC) and Enterohemorrhagic E. coli (EHEC).
The identification of the O157:H7 strain, a Shiga toxin-producing E. coli, further highlighted the species’ potential to cause serious public health issues. This discovery cemented E. coli’s status as a dual-natured organism—both a common, helpful part of the microbiota and a potential agent of severe disease. Ongoing study explores the mechanisms by which these distinct strains evolve and cause illness.