Question: What year did Van Leeuwenhoek discover micro-organisms?
About the article "Microscope", section "Rise of modern light microscopy".

Candidate passages:
Bacteria were first detected under the microscopes of Antony van Leeuwenhoek in the 17th century.
Leeuwenhoek, a Dutch scientist, performed many experiments testing and observing bacteria.
He observed plaque on his own teeth— “a little white matter” as he called it.
Under microscopes he saw “that in the said matter there were many very little living animalcules, very prettily a-moving,” which was the first sighting of oral bacteria as we know it.
Leeuwenhoek tested the mouths of others, as well as his own.
Two men that he tested had never cleaned their teeth in their lives and Leeuwenhoek found “an unbelievably great company of living animalcules…in such enormous numbers, that all the water…seemed to be alive.” Thus Leeuwenhoek discovered oral bacteria or “animalcules,” the name he gave bacteria in general.
Later studies have shown that he actually saw mats of bacteria, what we know today as biofilms.
Biofilms are communities of bacteria, or micro-organisms, attached to surfaces in the body.
Oral biofilms are more commonly referred to as plaque.
Biofilms form almost everywhere bacteria are.
In the mouth, they naturally form on any stationary surface, namely teeth, gums, and the tongue.
Leeuwenhoek made important findings of bacteria with his first observation and analysis of dental plaque, and since then much more has been discovered about the mouth and its ecology. 
van Leeuwenhoek created at least 25 microscopes, of differing types, of which only nine survive.
His simple microscopes were made of silver or copper frames, holding hand-ground lenses.
Those that have survived are capable of magnification up to 275 times.
It is suspected that Van Leeuwenhoek possessed units that could magnify up to 500 times.
Using his handcrafted microscopes, he was the first to observe and describe single-celled organisms, which he originally referred to as "animalcules", and which now referred to as micro-organisms or microbes. 
In 1676, Anton van Leeuwenhoek, who lived for most of his life in Delft, Holland, observed bacteria and other microorganisms using a single-lens microscope of his own design.
While Van Leeuwenhoek is often cited as the first to observe microbes, Robert Hooke made the first recorded microscopic observation, of the fruiting bodies of molds, in 1665.
It has, however, been suggested that a Jesuit priest called Athanasius Kircher was the first to observe micro-organisms.
He was among the first to design magic lanterns for projection purposes, so he must have been well acquainted with the properties of lenses.
One of his books contains a chapter in Latin, which reads in translation – ‘Concerning the wonderful structure of things in nature, investigated by Microscope.’ Here, he wrote ‘who would believe that vinegar and milk abound with an innumerable multitude of worms.’ He also noted that putrid material is full of innumerable creeping animalcule.
These observations antedate Robert Hooke’s Micrographia by nearly 20 years and were published some 29 years before van Leeuwenhoek saw protozoa and 37 years before he described having seen bacteria.
The field of bacteriology (later a subdiscipline of microbiology) was founded in the 19th century by Ferdinand Cohn, a botanist whose studies on algae and photosynthetic bacteria led him to describe several bacteria including "Bacillus" and "Beggiatoa".
Cohn was also the first to formulate a scheme for the taxonomic classification of bacteria and discover spores.
Louis Pasteur and Robert Koch were contemporaries of Cohn’s and are often considered to be the father of microbiology and medical microbiology, respectively.
Pasteur is most famous for his series of experiments designed to disprove the then widely held theory of spontaneous generation, thereby solidifying microbiology’s identity as a biological science.
Pasteur also designed methods for food preservation (pasteurization) and vaccines against several diseases such as anthrax, fowl cholera and rabies.
Koch is best known for his contributions to the germ theory of disease, proving that specific diseases were caused by specific pathogenic micro-organisms.
He developed a series of criteria that have become known as the Koch's postulates.
Koch was one of the first scientists to focus on the isolation of bacteria in pure culture resulting in his description of several novel bacteria including "Mycobacterium tuberculosis", the causative agent of tuberculosis.
While Pasteur and Koch are often considered the founders of microbiology, their work did not accurately reflect the true diversity of the microbial world because of their exclusive focus on micro-organisms having direct medical relevance.
It was not until the late 19th century and the work of Martinus Beijerinck and Sergei Winogradsky, the founders of general microbiology (an older term encompassing aspects of microbial physiology, diversity and ecology), that the true breadth of microbiology was revealed.
Beijerinck made two major contributions to microbiology: the discovery of viruses and the development of enrichment culture techniques.
While his work on the Tobacco Mosaic Virus established the basic principles of virology, it was his development of enrichment culturing that had the most immediate impact on microbiology by allowing for the cultivation of a wide range of microbes with wildly different physiologies.
Winogradsky was the first to develop the concept of chemolithotrophy and to thereby reveal the essential role played by micro-organisms in geochemical processes.
He was responsible for the first isolation and description of both nitrifying and nitrogen-fixing bacteria.
French-Canadian microbiologist Felix d'Herelle co-discovered bacteriophages and was one of the earliest applied microbiologists. 
The first detailed account of the interior construction of living tissue based on the use of a microscope did not appear until 1644, in Giambattista Odierna's "L'occhio della mosca", or "The Fly's Eye".
It was not until the 1660s and 1670s that the microscope was used extensively for research in Italy, The Netherlands and England.
Marcelo Malpighi in Italy began the analysis of biological structures beginning with the lungs.
Robert Hooke's "Micrographia" had a huge impact, largely because of its impressive illustrations.
The greatest contribution came from Antonie van Leeuwenhoek who discovered red blood cells and spermatozoa and helped popularise microscopy as a technique.
On 9 October 1676, Van Leeuwenhoek reported the discovery of micro-organisms.
In 1893 August Köhler developed a key technique for sample illumination, Köhler illumination, which is central to modern light microscopy.
This method of sample illumination gives rise to extremely even lighting and overcomes many limitations of older techniques of sample illumination.
Further developments in sample illumination came from Frits Zernike in 1953 for inventing Phase Contrast, and Georges Nomarski 1955 for his development of differential interference contrast illumination; both of which allow imaging of unstained, transparent samples.
Antonie Philips van Leeuwenhoek (, ; October 24, 1632 – August 26, 1723) was a Dutch tradesman and scientist.
He is commonly known as "the Father of Microbiology", and considered to be the first microbiologist.
He is best known for his work on the improvement of the microscope and for his contributions towards the establishment of microbiology.
Raised in Delft, Netherlands, Leeuwenhoek worked as a draper in his youth, and founded his own shop in 1654.
He made a name for himself in municipal politics, and eventually developed an interest in lensmaking.
Using his handcrafted microscopes, he was the first to observe and describe single-celled organisms, which he originally referred to as "animalcules", and which are now referred to as microorganisms.
He was also the first to record microscopic observations of muscle fibers, bacteria, spermatozoa, and blood flow in capillaries (small blood vessels).
Leeuwenhoek did not author any books; his discoveries came to light through correspondence with the Royal Society, which published his letters.