"I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. The biggest sort. . . had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort. . . oft-times spun round like a top. . . and these were far more in number." - Antonie van Leeuwenhoek 1683
What is microbiology?
There are several aspects to microbiology:
- The study of cells and how they work
- The study of microorganisms, cells capable of an independant existence, especially bacteria
- The study of microbial diversity, ecology and evolution
- The study of the function of microorganisms, in the world, in human society, in our bodies and in the bodies of plants and animals
As an applied biological science, microbiology deals with many practical problems in medicine, agriculture and industry. The rapidly evolving discipline of biotechnology is a direct product of microbiological study.
Microbiology can be subdivided into 4 major fields:
Major events in the history of microbiology
The existence of creatures too small to see had long been suspected, but it wasn't until the invention of the microscope that their study was enabled. Robert Hooke described the fruiting bodies of moulds in 1664, but the first person to describe microorganisms in detail was the Dutch amateur microscopopist Antonie van Leeuwenhoek. In 1673 Leeuwenhoek began reporting his findings in letters to the Royal Society of London which published them in English translation. He wrote many times to the society over a period of 50 years, the quote at the beginning of this write-up is from a letter dated 17th September 1683 in which he wrote about his microscopic investigation of dental plaque.
Leeuwenhoek's "animalcules" were infact bacteria.
Despite Leeuwenhoek's work microbiology did not really make any great progress until the 19th century by which time advances in the other sciences allowed for higher quality lab equipment, and the production of more accurately ground lenses allowed for the construction of much more advanced microscopes.
In the late 19th century, the investigation of two important questions laid the foundations for the science of microbiology as we know it today.
Does "spontaneous generation" occur?
If you leave an apple out, it will rot. If you examine the rotting apple microscopically you will find it to be teeming with microbial life. Some people believed that the microbes entered the apple from seeds or germs carried in the air, others believed that they arose from non-living material with no outside influence, so-called "spontaneous generation".
The most powerful opponent of spontaneous generation was French chemist Louis Pasteur. Pasteur was able to demonstrate that structures present in the air closely resembled those found on putrefying materials. He did this by passing air through guncotton filters, the particles in the air were trapped by the guncotton fibres and when the guncotton was dissolved using a mixture of alcohol and ether the particles could be collected and examined under a microscope. Pasteur found a number of structures ranging in size from 0.01mm to more than 1mm. We know now that these structures were the spores of common moulds and the cysts of protozoa. Pasteur found 1-2 structures per litre of air and under the microscope they were indistinguishable from those found in much larger numbers on putrefying material. He postulated that these structures are constantly being deposited on all objects, and if you were to treat food in such a way as to destroy these structures it would not rot.
Pasteur used heat to destroy these structures and found that indeed putrefication was prevented. This did not impress the adherants to spontaneous generation theory and they criticised his experiments, claiming that air was required for sponteous generation and by heating it Pasteur had somehow changed it.
Pasteur sidestepped their criticisms by constructing a swan-necked flask, now known as a "Pasteur flask". In the flask putrifying materials could be heated to boiling and allowed to cool. The curved neck of the flask allowed air to re-enter but the bends in the neck prevented particulates, bacteria and other microbes from getting into the main body of the flask. The material in the flask never rotted, and no microbes ever generated as long as the neck of the flask remained intact. However, if the neck was broken the material quickly putrified and the liquid was soon teeming with microorganisms.
This single experiment settled the spontaneous generation question.
What is the nature of contagious disease?
As early as the 16th century it was thought that something could be transmitted from a diseased person to a healthy person and induce disease in the well individual. Many diseases spread through populations and were known as contagious, the unknown thing that did the spreading was called the contagion.
After the discovery of microorganisms it was widely held that these organisms were the contagion, but proof was lacking. The work of Ignaz Semmelwies and Joseph Lister provided some evidence, but it was not until 1872 and the work of Robert Koch that the germ theory of disease was placed on a firm footing.
Koch studied Anthrax, a disease of cattle that could also be contracted by humans, he established that the bacteria Bacillus anthracis was always present in the blood of diseased cattle. However, the presence of the bacteria in the diseased animal was not enough to prove that it caused the disease, it may have been a result of the disease itself.
Koch demonstrated that it was possible to take a small sample of blood from a diseased animal, inject it into a healthy animal which then became ill and died. He could then take blood from this second animal, inject it into a third and obtain the same result, the third animal showed the same symptoms as the first. He repeated this as many as 20 times, and the 20th animal exhibited the same disease and died as rapidly as the first. In each case, through microscopic examination of the blood of the diseased animal he found the same bactera, B. anthracis. This experiment proved that the bacteria caused anthrax. Koch took this experiment further, he found that the bacteria could be grown in nutrient solution and after many transfers in culture, inoculating an animal with the solution produced the disease.
These experiments allowed the formulation of Koch's Postulates which supply the means of demonstrating that certain organisms cause disease. Koch's work wasn't accepted by the scientific community at large until Louis Pasteur demonstrated his anthrax vaccine in 1882.
The 20th Century
The 20th century has yielded great advances in the study and understanding of the microbial world, that without the work of Pasteur and Koch would not have been possible. Pasteur showed that heat could be used to destroy microbial cells, resulting in the sterilisation of growth-supporting media and Koch developed the first methods for the growth of pure microbial cultures. These discoveries enabled others to produce a number of important practical advances and brought about the revolution in molecular biology.
We now have a comprehensive understanding of the biological bases of infection, disease, host-microbe/host-parasite interactions, epidemiology, the mechanisms of inate and acquired resistance. We are able to utilise microbes to mass-produce useful proteins and compounds (insulin can be produced by genetically-modified strains of E. coli), to extract materials (copper can be extracted from ore by using Thiobacillus ferrooxidans), and to breakdown waste products and pollutants (the use of Burkholderia cepacia to breakdown the herbicide 2,4-dichlorophenyoxy acetic acid).
Microbiological research is sure to continue for many many years, the techniques and tools will be refined and we will see, understand and be able to manipulate more and more of the microbial world.
It is important that he research continues, the emergence of new diseases (for example Ebola, HIV, and Hanta) and the re-emergence of old ones (for example Tuberculosis, Typhoid and Diphtheria) ensures a need for the work of clinical and public health scientists.
The need to preserve our environment will lead us to look into novel ways of cleaning up pollution.
The drive to mass produce materials and medicines cheaply and cleanly will spur biotechnologists onwards.
As our understanding of microbial genetics increases, as we sequence and map more genomes our ability to manipulate, combat and utilise microbes will increase. Where 20th century microbiology gave birth to the field of molecular biology, the 21st century will see molecular biologists develop and refine the tools microbiologists need to further their research.
Biology of Microorganisms. Brock et al. Prentice Hall International. 1994
Medical Microbiology. Mims, C. et al Mosby 1993