by Daniel P. Haeusser
Figure 1A. Koch’s photograph of B. anthracis, one of several photomicrographs in his 1877 paper, the earliest published bacteria photos. Source.
Robert Koch is one of the key figures in early bacteriology, helping develop culture techniques (e.g. solid media), critical reasoning (e.g. Koch’s postulates), and disease etiology (e.g. cholera and tuberculosis). He also published the first photomicrographs of bacteria (Figure 1A) in his 1877 paper Verfahren zur Untersuchung, zum Conservieren und Photographiren der Bakterien.
Discontent with communicating microscopic observations with hand-drawn illustrations, Koch pioneered the photography of bacteria. On suitable days, Koch would set up to shoot outdoors. In his 1877 publication Koch explains how to take photographs outside through a basic microscope:
“Clean all the lenses, screw them in completely, and place the illuminating mirror on the sunny side of the microscope. With a dark cloth over your head, look through the ground glass and adjust the light and focus the specimen… Once the image is in focus… go inside to prepare the photographic plates. In the darkroom…remove a clean glass plate with forceps and pour over its surface the iodized collodion solution, making sure the film spreads evenly and completely. Once the collodion film is ready, close the darkroom door and carefully lower the plate into the silver bath… Allow it to drain and put it in the cassette… Go back outdoors to the photomicrographic apparatus. Remove the black cloth…and check to be certain that the proper image is still in focus… Then carefully place the cassette, being careful not to move anything. After the exposure… push the slide back in the cassette, remove the cassette from the microscope, and cover the microscope again with the black cloth. This whole procedure must be done quickly! Run back to the darkroom with the closed cassette, develop the plate, and fix the negative. If the photographic image is not completely sharp, or if there are imperfections in the emulsion… it is necessary to repeat the whole process, since nothing is more disheartening in the photographic technique than to try to make prints from unsatisfactory negatives.1
Quite a process! Following this protocol, Koch reports it took at least three hours to obtain four to six good pictures. Note that this time does not include setting up the equipment, preparing the bacterial sample, or freshly mixing the photographic chemicals. Yet with skill, patience, and perseverance during his early studies on anthrax, Koch obtained photos of the Gram-positive B. anthracis in a quality that rivals images taken today. Indeed, as an exercise of curiosity, members of my department2 took an Instagram picture of B. anthracis using a cell phone camera. The image took seconds to capture with modern technology, yet doesn’t come close to rivaling Koch’s.
Koch’s realization of bacterial photography was not merely a pretty picture. The communication of accurate images of bacterial shape was vital to the understanding that multiple species of bacteria existed, and Koch’s practice in imaging relatively easy-to-cultivate organisms like B. anthracis allowed his eventual rapid success in discovering the extremely fastidious M. tuberculosis in diseased tissue. It is this attention to detail and scientific resolve that led Koch to the discoveries that have immortalized him in scientific, medical, and indeed general human history (Figure 1B).
1 Brock, Thomas D. (1999) Robert Koch: A Life in Medicine and Bacteriology. ASM Press, p. 61.
2 Thanks are given to Katie McCallum for her Instagram account and to Lori Horton, Malik Raynor, and Michelle Swick of the Kohler Lab for the microscopy equipment and B. anthracis sample.