Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Boyer, Herbert Wayne

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of the organism, typically when hands dirty from outdoor play

are put into the mouth.

The latter means of acquiring botulism involves the

form of the bacterium known as a spore. A spore is a biologi-

cally dormant but environmentally resilient casing around the

bacterium’s genetic material. The spore form allows the

organism to survive through prolonged periods of inhospitable

conditions. When conditions improve, such as when a spore in

soil is ingested, resuscitation, growth of the bacterium, and

toxin production can resume. For example, foodborne botu-

lism is associated with canned foods where the food was not

heated sufficiently prior to canning to kill the spores.

Botulism is relatively rare. In the United States, just

over 100 cases are reported each year, on average. The num-

ber of cases of foodborne and infant botulism has not changed

appreciably through the 1990s to the present day. Foodborne

cases have tended to involve the improper preparation of

home-canned foods.

There are seven known types of botulism toxin, based

on their antigenic make-up. These are designated toxins A

through G. Of these, only types A, B, E, and F typically cause

botulism in humans, although involvement of type C toxin in

infants has been reported, and may be particularly associated

with the consumption of contaminated honey.

Infant botulism caused by toxin type C may be different

from the other types of botulism in that the toxin is produced

in the person following the ingestion of living Clostridium

botulinum.

The toxins share similarities in their gross structure and

in their mechanism of action. The toxins act by binding to the

region of nerve cells that is involved in the release of a chem-

ical known as a neurotransmitter. Neurotransmitters travel

across the gap (synapse) separating neurons (nerve cells) and

are essential to the continued propagation of a neural impulse.

Accordingly, they are vital in maintaining the flow of a trans-

mitted signal from nerve to nerve. Blocking nerve transmis-

sions inhibits the means by which the body can initiate the

movement of muscles. The result is paralysis. This paralysis

produces a variety of symptoms including double or blurred

vision, drooping eyelids, slurred speech, difficulties in swal-

lowing, muscle weakness, paralysis of limbs and respiratory

muscles.

The appearance of the symptoms of botulism vary

depending on the route of toxin entry. For example, ingestion

of toxin-contaminated food usually leads to symptoms within

two to three days. However, symptoms can appear sooner or

later depending on whether the quantity of toxin ingested is

low or high.

The diagnosis of botulism and so the start of the appro-

priate therapy can be delayed, due to the relative infrequency

of the malady and its similarity (in the early stages) with other

maladies, such as Guillain-Barré syndrome and stroke.

Diagnosis can involve the detection of toxin in the patient’s

serum, isolation of living bacteria from the feces, or by the

ability of the patient’s sample to produce botulism when intro-

duced into test animals.

Clostridium botulinumrequires an oxygen-free atmo-

sphere to grow. Growth of the bacteria is associated with the

production of gas. Thus, canned foods can display a bulging

lid, due to the build-up of internal pressure. Recognition of

this phenomenon and discarding of the unopened can is

always a safe preventative measure.

Studies conducted by United States health authorities

have shown that the different forms of the botulism toxin dis-

play some differences in their symptomatology and geo-

graphic distribution. Type A associated botulism is most

prevalent in the western regions of the US, particularly in the

Rocky Mountains. This toxin produces the most severe and

long-lasting paralysis. Type B toxin is more common in the

eastern regions of the country, especially in the Allegheny

mountain range. The paralysis produced by type B toxin is less

severe than with type A toxin. Type E botulism toxin is found

more in the sediments of fresh water bodies, such as the Great

Lakes. Finally, type F is distinctive as it is produced by

Clostridium baratii.

Treatment for botulism often involves the administra-

tion of an antitoxin, which acts to block the binding of the

toxin to the nerve cells. With time, paralysis fades. However,

recovery can take a long time. If botulism is suspected soon

after exposure to the bacteria, the stomach contents can be

pumped out to remove the toxic bacteria, or the wound can be

cleaned and disinfected. In cases of respiratory involvement,

the patient may need mechanical assistance with breathing

until lung function is restored. These measures have reduced

the death rate from botulism to 8% from 50% over the past

half century.

As dangerous as botulinum toxin is when ingested or

when present in the bloodstream, the use of the toxin has been

a boon to those seeking non-surgical removal of wrinkles.

Intramuscular injection of the so-called “Botox” relaxes mus-

cles and so relieves wrinkles. Thus far, no ill effects of the cos-

metic enhancement have appeared. As well, Botox may offer

relief to those suffering from the spastic muscle contractions

that are a hallmark of cerebral palsy.

See alsoBacteria and bacterial diseases; Bioterrorism; Food

safety

BOVINE SPONGIFORM ENCEPHALOPATHY

(BSE)• seeBSE ANDCJD DISEASE

BBoyer, Herbert WayneOYER, HERBERTWAYNE(1936- )

American molecular geneticist

In 1973 Herbert Boyer was part of the scientific team that first

described the complete process of genesplicing, which is a

basic technique of genetic engineering (recombinant DNA).

Gene splicing involves isolating DNA, cutting out a piece of it

at known locations with an enzyme, then inserting the frag-

ment into another individual’s genetic material, where it func-

tions normally.

Boyer was born in Pittsburgh and received a bachelor’s

degree in 1958 from St. Vincent College. At the University of

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