Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Schick, Bela

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The vulnerable foods offer Salmonellaa ready source of

nutrients and moisture. If the temperature conditions are right

for growth, the increase in numbers of Salmonellacan be

explosive. For example, from a starting population of a single

live bacterium with a division time of 30 minutes, a population

of over 500 million bacteria can be generated in just 15 hours.

The ingestion of contaminated foods leads, within

hours, to the development of one or all of the following ail-

ments: stomach cramps, vomiting, fever, headache, chills,

sweating, fatigue, loss of appetite, and watery or bloody diar-

rhea. Prolonged diarrhea is dangerous, as the body can be

depleted of fluids and salts that are vital for the proper func-

tioning of organs and tissues. The resulting shock to the body

can be intolerably lethal to infants and the elderly. As well,

there is a possibility that the bacteria can spread from the

intestinal tract to the bloodstream, leading to infections in

other parts of the body.

There are hundreds are different forms, or strains, of

Salmonella,varying in the antigenic composition of their outer

surface and in the maladies caused. Concerning food poison-

ing, Salmonella enteriditisis of particular concern. This strain

causes gastroenteritisand other maladies because of several

so-called virulence factors the organism is armed with.

One virulence factor is called adhesin. An adhesin is a

molecule that functions in the recognition and adhesion of the

bacterium to a receptor on the surface of a host cell. In the case

of Salmonella,the tube-like structures called fimbriae can per-

form this function. Other molecules on the surface of the bac-

terium can be involved also.

Another virulence factor is a compound called

lipopolysaccharide (LPS for short). Depending on the struc-

ture, LPS can help shield the Salmonellasurface from host

antibacterial compounds. As well, part of the LPS, can lipid

A, can be toxic to the host. The lipid A toxic component is

also referred to as endotoxin. Salmonella also produces

another toxin called enterotoxin. Other bacteria produce

enterotoxin as well. The Salmonellaenterotoxin is readily

degraded by heat, so proper cooking of food will destroy the

activity of the toxin. The enterotoxin remains inside the bac-

teria, so the toxin concentration increases with the increase in

bacterial numbers.

Salmonellais not particularly difficult to identify, as it

produces distinctive visual reactions on standard laboratory

growth media. For example, on bismuth sulfide media the bac-

teria produce hydrogen sulfide, which produces jet-black

colonies. Unfortunately for the individual who experiences a

food poisoning event, the diagnosis is always “after the fact.”

Knowledge of the cause often comes after the miseries of the

poisoning have come and gone. But, in those instances where

the spread of the bacteria beyond the gastrointestinal tract has

occurred, diagnosis is helpful to treat the infection.

The prospects of eliminating of Salmonellafood poi-

soning using vaccinationare being explored. The most prom-

ising route is to block the adhesion of the bacteria to host

epithelial cells of the intestinal tract. Such a strategy would

require the development of a vaccinewith long lasting immu-

nity. However, vaccine development efforts will likely be

devoted to other illnesses. For the foreseeable future, the best

strategy in preventing Salmonellafood poisoning will remain

the proper cooking of foods and the observance of good

hygiene practices when handling food.

See alsoFood preservation

SCANNING ELECTRON MICROSCOPE•see

ELECTRON MICROSCOPE, TRANSMISSION AND SCANNING

SSchick, Bela CHICK, BELA(1877-1967)

Hungarian-born American physician

Bela Schick was a pioneer in the field of child care; not only

did he invent the diphtheriatest, which helped wipe out this

disease in children, but he also formulated and publicized

child care theories that were advanced for his day. Schick also

defined the allergic reaction, was considered the leading pedi-

atrician of his time, and made contributions to knowledge

about scarlet fever, tuberculosis, and infant nutrition. Schick

received many honors for his work, including the Medal of the

New York Academy of Medicine and the Addingham Gold

Medal, a British award. Schick was also the founder of the

American Academy of Pediatrics.

Schick was born on July 16, 1877 in Boglar, Hungary, the

child of Jacob Schick, a grain merchant, and Johanna Pichler

Schick. He attended the Staats Gymnasium in Graz, Austria,

graduating in 1894. He then received his M.D. degree at Karl

Franz University, also in Graz. After a stint with the medical

corps in the Austro-Hungarian army, Schick started his own

medical practice in Vienna in 1902. From then on he devoted his

ample energies to teaching, research, and medical practice at the

University of Vienna, where he served from 1902 to 1923—first

as an intern, then as an assistant in the pediatrics clinic, and

finally as lecturer and professor of pediatrics.

It was in 1905 that Schick made one of his most signif-

icant contributions. While working with collaborator Clemens

von Pirquet, Schick wrote his first research study describing

the phenomenon of allergy, which was then called serum sick-

ness. The study not only described the concept of allergy, but

also recommended methods of treatment.

At age 36, Schick moved on to make one of the most

important discoveries of the twentieth century—the test for

diphtheria. The test, announced in 1913, was a remarkably

simple one that could tell whether a person was vulnerable to

the disease. It showed whether a patient had already been

exposed to the diphtheria toxin, which would make him

immune from getting it again. A tiny amount of the diluted

toxin was injected into the patient’s arm. If the spot turned red

and swollen, the doctors would know whether or not the

patient been exposed to the disease. The treatment was then

injection with an antitoxin.

Diphtheria was a common disease in the early twentieth

century and afflicted thousands of children in every city

throughout the world. It was especially common in Europe,

where the close quarters of many cities made infection more

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