Life has changed since the Dutch botanist Anthonie van Leeuwenhoek (1632-1723) revealed
the diversity and ubiquity of the microbial world through the discovery of microscopy.
Van Leeuwenhoek can be considered to be the fi rst genuine microbiologist. Microscopic
evidence provided support for the emerging germ theory of disease in the 19th century. In
the 1880s, Robert Koch defi ned his postulates for determining whether or not a microorganism
is the etiological agens of a disease. Since the 19th century, advances in knowledge have
included the discovery of viruses, chlamydiae, mycoplasmata and rickettsiae as new classes
of microorganisms that cannot (yet) be grown in pure culture, but require living cells for reproduction.
The spectrum of bacterial, fungal and protozoan pathogens has been expanding
with improved culture techniques and the development of advanced imaging techniques.
However, the most revolutionary advance in biomedical science since Van Leeuwenhoek, is
due to the discovery of nucleic acids in 1871 by Miescher, which lead to the discovery of DNA
as the source of genetic information and as the basis for characterization of an organism in
1953 by Watson, Crick and Wilkin