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Institut Pasteur, Paris, France

48° 50′ 24″ N, 2° 18′ 42″ E

The Founder of Immunology

The French chemist and microbiologist Louis Pasteur is a household name because of the pasteurization of milk and other liquids. But Pasteur originally started out doing a doctorate on crystallography. He went on to disprove the theory of spontaneous generation (that bacteria and other living creatures such as maggots could appear from nowhere), and later showed how to create vaccinations using weakened forms of live diseases.

The Institut Pasteur is a private foundation that performs fundamental biological research. Pasteur is buried inside the institute, and the rooms he lived in during the last part of his life have been turned into a museum. Pasteur’s home consisted of 10 rooms and two galleries with a grand staircase linking them, and it has been entirely restored to the state it was in when Pasteur was alive.

The museum is partly historical and partly scientific. The general living spaces show the comfortable life Pasteur and his wife enjoyed in the large apartment, and Pasteur’s crypt is a Byzantine funeral chamber under the building. Of interest to scientists is an entire room dedicated to Pasteur’s equipment and specimens.

Pasteur’s crystallography work looked at tartaric acid (C4H6O6), which occurs naturally in wine. Tartaric acid is chiral—it exists in two crystal forms that are mirror images of each other, yet cannot be superimposed (like human hands). One form rotates light to the left, the other to the right.

Pasteur went on to realize that the left-handed form of tartaric acid would aid fermentation, but the right-handed form would not. This led him to study fermentation, eventually demonstrating that it is caused by micro-organisms (called ferments) and that those organisms could be isolated and studied.

He then set out to discover where the ferments came from, and was able to show that they were present in the air or dust and were not spontaneously created. He did this with a simple experiment wherein a specially made bottle with a long curving neck was filled with meat broth. The neck allowed air to pass, but prevented dust from entering, and Pasteur observed that the broth did not ferment. (Some of these bottles remain, their contents still untouched, 150 years later.)

Further, he showed that if care was taken to isolate a specimen from micro-organisms, it would not ferment or rot. He then went on to show that some micro-organisms needed air to survive, and others did not (or even were harmed by the presence of oxygen).

These discoveries led him to study diseases, and he isolated the bacterium staphylococcus, streptococcus, and pneumococcus (see Figure 11-1).

Figure 11-1. Pneumococcus (Image credit: CDC/Janice Carr)

At the time, the idea of vaccination against smallpox (using cowpox) was well known, having been popularized by Edward Jenner (see Chapter 44) in the late 1700s. Pasteur took this a step further by showing how to attenuate live viruses so that they could be used for vaccination. He successfully reduced the virulence of cholera, anthrax, and rabies and used them as vaccines.

Practical Information

Information for the Institut Pasteur is at http://www.pasteur.fr/english.html, and guided tours are available. There is printed information in English, and the room containing Pasteur’s scientific instruments has a special audio commentary in English.

The museum is easy to reach: there’s a stop named Pasteur on the Paris Metro lines 6 and 12.

Pasteurization, Flash Pasteurization, and UHT

Once Pasteur had realized that fermentation and diseases were caused by micro-organisms, he also realized that it was possible to kill the micro-organisms (or significantly reduce their number) by heating. Pasteur showed that heating wine to 55ºC prevented wine diseases and stopped fermentation.

The basic process of pasteurization is still used today. Milk can undergo one of three processes to remove pathogens: pasteurization, flash pasteurization, or UHT.

Basic pasteurization involves heating milk to 63ºC for 30 minutes in a large vat. This is hot enough and long enough to kill or attenuate Mycobacterium tuberculosis (the bacteria responsible for tuberculosis) and other bacteria that are relatively heat-resistant. At the same time, the overall quality of the milk is not spoiled.

Flash pasteurization (which is also used for fruit juices) is sometimes called High Temperature Short Time, and involves heating milk to 72°C for 15 seconds. This also preserves the quality of the milk and kills off harmful bacteria. It is performed by forcing the milk through small heated pipes, or between hot metal plates, to obtain the necessary rapid rise in temperature.

Neither of these processes sterilizes the milk. There are still some micro-organisms remaining, although they have been greatly reduced in number and will not cause disease in humans. Because micro-organisms are still present, the milk must be kept refrigerated to maintain its freshness.

UHT treatment, on the other hand, raises the temperature of the milk to 138°C for one or two seconds and does almost entirely sterilize it. UHT milk (sometimes called shelf milk) is packed in sterile containers and can last for months unrefrigerated. However, the taste of the milk is altered, giving it a cooked flavor not present with pasteurization.

Recently, pasteurization of milk has been replaced by the use of filters. Since bacteria are typically a few micrometers long, it’s possible to remove them using a filter with smaller holes (of around 1 micrometer). At the same time, the constituent parts of milk are even smaller (proteins can be as small as 1 nanometer) and can pass through the filter.

Filtration of milk brings pasteurization full circle—when Pasteur was investigating the existence of micro-organisms, he used filters in his broth experiments to keep micro-organisms out. In addition, his research drove the creation of ceramic water filters, since they were then known to protect against disease.