It was Koch who first adapted staining methods to better see bacteria under the microscope. Basic dyes like methylene blue will chemically bond to bacteria and make them more visible.
The hair like projections, flagella that make some bacteria move were first seen by Koch using special staining process. He used special oil on his slides to improve lighting at higher magnification and added another lens developed by Abbe to the microscope to better channel the light through the lenses.
We use both oil and the Abbe condenser lens on microscopes in microbiological work today. The technique of smearing bacteria on a clean glass slide followed by a slight heating to kill and stick the cells to the glass was developed by Koch.
In 1881, he presented the Royal Society with another breakthrough so grand that Pasteur met with him after the presentation with the greeting, “C’est un grand progress, Monsieur!” (“This is great progress, sir!”).
Until this point, bacteria had been grown in the lab in broth or on the surface of potato slices sterilized by hot air (also invented by Koch!). Koch found that by adding the protein gelatin to beef broth it could be solidified and the bacteria more clearly seen and separated.
Because this medium could contain a greater variety of nutrients than potato medium, it was possible to grow a. greater variety of bacteria.
The major problem with his method was that a number of bacteria could digest gelatin. When grown on the gelatin media, these bacteria would form little puddles which made it difficult to identify individual characteristics.
This problem was solved when a coworker’s wife told Koch about a solidifying agent she used in cooking called agar-agar. The chemical comes from seaweed, algae, and was the perfect answer to the problem because most microbes cannot digest agar-agar.
Today this material is used worldwide to solidify bacteriological media. It is so common that many use only the term “agar” to refer to the solid nutrient agar-agar growth medium.
However, nobody is perfect, not even Robert Koch! In 1882, Pasteur developed a theory and a method for vaccinating animals against anthrax. He presented his ideas at a scientific meeting which included Koch. Koch vigorously opposed Pasteur’s idea in person and though correspondence.
The argument between them continued even while Pasteur began field testing his vaccine and method. Koch’s letters of opposition soon faded as Pasteur’s successes continued to rise. However, this minor setback did not discourage Koch.
He continued his work and discovered the bacterium that causes cholera (Vibrio cholerae) and isolated the bacterium that causes tuberculosis (Mycobacterium tuberculosis).
The following appeared in the May 1882 edition of Scientific American and recounts Robert Koch’s efforts, which confirmed that the bacterium Mycobacterium tuberculosis is the cause of the disease once known as the “wasting disease.”
“Professor Tyndall has communicated to the London Times as account of results obtained by Dr. Koch of Berlin in the investigation of the etiology of tubercular disease, as set forth by him in an address delivered on March 24 before the Physiological Society of Berlin.
In pursuing these investigations Dr. Koch subjected the diseased organs of a great number of men and animals to microscopic examination, and he found in all cases the tubercles were infested with a minute, rod-shaped parasite, which, by means of a special dye, he differentiated from the surrounding tissue.
Transferring directly, by inoculation, the tuberculous matter from diseased animals to healthy ones, he in every instance reproduced the disease. Dr. Koch has examined the matter expectorated from the lungs affected with phthisis and found in it swarms of bacilli, whereas in matter expectorated from the lungs of persons not thus affected he has never found the organism. Guinea pig infected with expectorated matter that had been kept dry for two, four or eight weeks were smitten with tubercular disease quite as virulent as that produced by fresh expectoration.”
Koch also worked with the bacterium that causes boils (Staphylococcus aureus), and with the cause of cattle plague (a virus infection). His single most outstanding contribution to all science has become known as Koch’s Postulates.
The Postulates state:
(1) a particular organism can always be found in association with a particular disease, but not in a healthy individual;
(2) the organism can be grown in the laboratory by itself; (3) this pure growing culture will produce the same disease when placed back into a new, susceptible animal; and
(4) it is possible to recover the organisms from this sick animal and grow them in pure culture. By using these postulates as guidelines, many microbiologists have proven that a particular organism is in fact the cause of a particular disease.