How microbiology began

Microbiology is the study of very small organisms. It began in the 1670s-1680s, when Antonie van Leeuwenhoek looked through his home-made microscopes and saw tiny moving creatures he called 'animalcules'.

Where did these microbes come from? Many people believed they arose from lifeless matter: spontaneous generation. Spallanzani found that broth that had been boiled and sealed stayed free of life, but critics said boiling had destroyed some 'vital force' in the air.

Louis Pasteur settled it with S-necked (swan-necked) flasks. Air could enter the flask, but dust and microbes were trapped in the curved neck. Boiled broth stayed clear for as long as the neck was intact. When the neck was broken, or the flask tipped so broth touched the trapped dust, microbes soon grew. So microbes come from outside, not from the broth. Pasteur disproved spontaneous generation, and proposed the germ theory of disease: microbes cause disease.

Robert Koch proved it. He grew a pure culture of a bacillus from animals with anthrax, injected it into healthy mice, and they developed anthrax. His postulates (rules) are still used to link a particular microbe to a particular disease. The late 1800s and early 1900s became the Golden Age of Microbiology.

Growing microbes needed good media:

• Pasteur's medium (1860) contained yeast, ash and ammonium salts; Cohn varied the sugars.
• Koch used meat extracts, and then wanted solid media to grow separate colonies. He tried slices of potato, then gelatin, and finally agar. He coined the word 'colony' for a visible clump of cells grown from one cell.
• Petri introduced his famous shallow dish in 1887.

Later came selective media (early 1900s), the discovery of growth factors (1930s), viruses seen with the electron microscope (1940s), and antibiotics added to media (1960s). Today microbes are living factories that make insulin, interferon, clotting factors and vaccines.