Microbiology and Immunology

Fleming, Alexander WORLD OF MICROBIOLOGY AND IMMUNOLOGY

218

•

depended on whatever enzymes might occur in “wild” yeast.

Today, wine-makers are able to select from a variety of spe-

cially cultured yeast that control the precise direction that fer-

mentation will take.

Ethyl alcohol is not the only useful product of fermen-

tation. The carbon dioxide generated during fermentation is

also an important component of many baked goods. When the

batter for bread is mixed, for example, a small amount of sugar

and yeast is added. During the rising period, sugar is fer-

mented by enzymes in the yeast, with the formation of carbon

dioxide gas. The carbon dioxide gives the batter bulkiness and

texture that would be lacking without the fermentation

process. Fermentation has a number of commercial applica-

tions beyond those described thus far. Many occur in the food

preparation and processing industry. A variety of bacteriaare

used in the production of olives, cucumber pickles, and sauer-

kraut from the raw olives, cucumbers, and cabbage, respec-

tively. The selectionof exactly the right bacteria and the right

conditions (for example, acidity and salt concentration) is an

art in producing food products with exactly the desired fla-

vors. An interesting line of research in the food sciences is

aimed at the production of edible food products by the fer-

mentation of petroleum.

In some cases, antibioticsand other drugs can be pre-

pared by fermentation if no other commercially efficient

method is available. For example, the important drug corti-

sone can be prepared by the fermentation of a plant steroid

known as diosgenin. The enzymes used in the reaction are pro-

vided by the moldRhizopus nigricans.

One of the most successful commercial applications of

fermentation has been the production of ethyl alcohol for use

in gasohol. Gasohol is a mixture of about 90% gasoline and

10% alcohol. The alcohol needed for this product can be

obtained from the fermentation of agricultural and municipal

wastes. The use of gasohol provides a promising method for

using renewable resources (plant material) to extend the avail-

ability of a nonrenewable resource (gasoline).

Another application of the fermentation process is in the

treatment of wastewater. In the activated sludge process, aerobic

bacteria are used to ferment organic material in wastewater. Solid

wastes are converted to carbon dioxide, water, and mineral salts.

See alsoHistory of microbiology; Winemaking

FERTILITY•seeREPRODUCTIVE IMMUNOLOGY

FILOVIRUSES•seeHEMORRHAGIC FEVERS AND

DISEASES

FIMBRIA•seeBACTERIAL APPENDAGES

FLAGELLA•seeBACTERIAL APPENDAGES

FLAVIVIRUSES•seeHEMORRHAGIC FEVERS AND DIS-

EASES

FFleming, Alexander LEMING, ALEXANDER(1881-1955)

Scottish bacteriologist

With the experienced eye of a scientist, Alexander Fleming

turned what appeared to be a spoiled experiment into the dis-

covery of penicillin.

Fleming was born in 1881 to a farming family in

Lochfield, Scotland. Following school, he worked as a ship-

ping clerk in London and enlisted in the London Scottish

Regiment. In 1901, he began his medical career, entering St.

Mary’s Hospital Medical School, where he was a prizewin-

ning student. After graduation in 1906, he began working at

that institution with Sir Almroth Edward Wright, a pathologist.

From the start, Fleming was innovative and became one of the

first to use Paul Ehrlich’s arsenic compound, Salvarsan, to

treat syphilisin Great Britain.

Wright and Fleming joined the Royal Army Medical

Corps during World War I and they studied wounds and infec-

tion-causing bacteriaat a hospital in Boulogne, France. At that

time, antisepticswere used to treat bacterial infections, but

Wright and Fleming showed that, especially in deep wounds,

bacteria survive treatment by antiseptics while the protective

white blood cells in the wound are destroyed. This creates an

even worse situation in which infection can spread rapidly.

Forever affected by the suffering he saw during the war,

Fleming decided to focus his efforts on the search for safe

antibacterial substances. He studied the antibacterial power of

the body’s own leukocytes contained in pus. In 1921, he dis-

covered that a sample of his own nasal mucus destroyed bac-

teria in a petri dish. He isolated the compound responsible for

the antibacterial action, which he called lysozyme, in saliva,

blood, tears, pus, milk, and in egg whites.

Fleming made his greatest discovery in 1928. While he

was growing cultures of bacteria in petri dishes for experi-

ments, he accidentally left certain dishes uncovered for several

days. Fleming found a moldgrowing in the dishes and began

to discard them, when he noticed, to his astonishment, that

bacteria near the molds were being destroyed. He preserved

the mold, a strain of Penicillium and made a cultureof it in a

test tube for further investigation. He deduced an antibacterial

compound was being produced by the mold, and named it

penicillin. Through further study, Fleming found that peni-

cillin was nontoxic in laboratory animals. He described his

findings in research journals but was unable to purify and con-

centrate the substance. Little did he realize that the substance

produced by his mold would save millions of lives during the

twentieth century.

Fleming dropped his investigation of penicillin and his

discovery remained unnoticed until 1940. It was then that

Oxford University-based bacteriologists Howard Florey and

Ernst Chain stumbled upon a paper by Fleming while

researching antibacterial agents. They had better fortune than

Fleming, for they were able to purify penicillin and test it on

humans with outstanding results. During World War II, the

drug was rushed into mass-production in England and the

United States and saved thousands of injured soldiers from

infections that might otherwise have been fatal.

womi_F 5/6/03 2:15 PM Page 218