Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Lancefield, Rebecca Craighill

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these surfaces. The luxuriant growth of these bacteria excludes

other bacteria from gaining a foothold. This phenomenon is

known as competitive exclusion.

Commercially, Lactobacillusis best known as the basis

of yogurt manufacture. A mixture of Lactobacillus bulgaricus

or Lactobacillus acidophilusand Streptococcus thermophilus

produce the lactic acid that ferments milk.

Yogurt that contains live bacteria usually contains

Lactobacillus acidophilus. There is evidence that the persist-

ence of the bacteria in the intestinal tract for up to a week after

consuming yogurt increases the number of antibody-secreting

cells in the intestine. Also Lactobacillus acidophilusbacteria

possess and enzyme called lactase that enables the bacteria are

to utilize undigested starches, particularly those in milk, that

would otherwise be eliminated from the body.

Yet another benefit of Lactobacillusis the production of

beneficial compounds that are used by the body. For example,

Lactobacillus acidophilusproduces niacin, folic acid, and

pyridoxine, a group of compounds that collectively are

referred to as the B vitamins.

Another noteworthy strain of Lactobacillusis known as

Lactobacillus GG. This strain was isolated from humans in the

1980s by Drs. Sherwood Gorbach and Barry Goldin. The ini-

tials of their last names are the basis for the GG designation.

Lactobacillus GGhas shown great promise as a nutritional

supplement because the bacteria are able to survive the pas-

sage through the very acidic conditions of the stomach. They

then colonize the intestinal tract. There, the bacteria produce a

compound that has antibacterial activity. This may help main-

tain the intestinal tract free from invading bacteria.

See alsoMicrobial flora of the stomach and gastrointestinal

tract; Probiotics

LANCEFIELD, REBECCACRAIGHILL

(1895-1981)Lancefield, Rebecca Craighill

American bacteriologist

Rebecca Craighill Lancefield is best-known throughout the

scientific world for the system she developed to classify the

bacteriaStreptococcus.Her colleagues called her laboratory at

the Rockefeller Institute for Medical Research (now

Rockefeller University) “the Scotland Yard of streptococcal

mysteries.” During a research career that spanned six decades,

Lancefield meticulously identified over fifty types of this bac-

teria. She used her knowledge of this large, diverse bacterial

family to learn about pathogenesis and immunityof its afflic-

tions, ranging from sore throats, rheumatic fever and scarlet

fever, to heart and kidney disease. The Lancefield system

remains a key to the medical understanding of streptococcal

diseases.

Born Rebecca Craighill on January 5, 1895, in Fort

Wadsworth on Staten Island in New York, she was the third of

six daughters. Her mother, Mary Montague Byram, married

William Edward Craighill, a career army officer in the Army

Corps of Engineers who had graduated from West Point.

Lancefield received a bachelor’s degree in 1916 from

Wellesley College, after changing her major from English to

zoology. Two years later, she earned a master’s degree from

Columbia University, where she pursued bacteriology in the

laboratory of Hans Zinsser. Immediately upon graduating

from Columbia, she formed two lifelong partnerships. She

married Donald Lancefield, who had been a classmate of hers

in a genetics class. She was also hired by the Rockefeller

Institute to help bacteriologists Oswald Avery and Alphonse

Dochez, whose expertise on Pneumococcuswas then being

applied to a different bacterium. This was during World War I,

and the project at Rockefeller was to discover whether distinct

types of Streptococcicould be isolated from soldiers in a

Texas epidemic so that a serum might be produced to prevent

infection. The scientists employed the same serological tech-

niques that Avery had used to distinguish types of

Pneumococcus.Within a year, Avery, Dochez, and Lancefield

had published a major report which described four types of

Streptococcus.This was Lancefield’s first paper.

Lancefield and her husband took a short hiatus to teach

in his home state at the University of Oregon, then returned to

New York. Lancefield worked simultaneously on a Ph.D. at

Columbia and on rheumatic fever studies at the Rockefeller

Institute in the laboratory of Homer Swift, and her husband

joined the Columbia University faculty in biology. Before

World War I, physicians had suspected that Streptococcus

caused rheumatic fever. But scientists, including Swift, had

not been able to recover a specific organism from patients.

Nor could they reproduce the disease in animals using patient

cultures. Lancefield’s first project with Swift, which was also

her doctoral work, showed that the alpha-hemolytic class of

Streptococcus,also called green or viridans, was not the cause

of rheumatic fever.

As a result of her work with Swift, Lancefield decided

that a more basic approach to rheumatic fever was needed. She

began sorting out types among the disease-causing class, the

beta-hemolytic streptococci. She used serological techniques

while continuing to benefit from Avery’s advice. Her major

tool for classifying the bacteria was the precipitin test. This

involved mixing soluble type-specific antigens, or substances

used to stimulate immune responses, with antisera (types of

serum containing antibodies) to give visible precipitates.

Precipitates are the separations of a substance, in this case bac-

teria, from liquid in a solution, the serum, in order to make it

possible to study the bacteria on its own.

Lancefield soon recovered two surface antigens from

these streptococci. One was a polysaccharide, or carbohydrate,

called the C substance. This complex sugar molecule is a major

component of the cell wall in all streptococci. She could further

subdivide its dissimilar compositions into groups and she des-

ignated the groups by the letters A through O. The most com-

mon species causing human disease, Streptococcus pyogenes,

were placed in group A. Among the group A streptococci,

Lancefield found another antigenand determined it was a pro-

tein, called M for its matt appearance in colonyformations.

Because of differences in M protein composition, Lancefield

was able to subdivide group A streptococci into types. During

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