Essentials of Anatomy and Physiology

simpler in structure than the bacteria. All viruses are
parasites because they can reproduce only within the
living cells of a host. Therefore, all viruses cause dis-
ease. Common human viral diseases are influenza, the
common cold, and chickenpox.
Protozoaare single-celled animals such as amoe-
bas. Most protozoa are free living in freshwater or
saltwater, where they consume bacteria, fungi, and one
another. Human protozoan parasites include those
that cause malaria, amebic dysentery, and giardiasis,
another intestinal infection.
Fungimay be unicellular or multicellular. Molds
and mushrooms are familiar fungi. They decompose
organic matter in the soil and freshwater and help
recycle nutrients. Fungal diseases of people include
yeast infections, ringworm, and more serious diseases
such as a type of meningitis.
Wormsare multicellular animals. Most are free liv-
ing and non-pathogenic; within the soil they consume
dead organic matter or smaller living things. Worm
infestations of people include trichinosis, hookworm
disease, and tapeworms.
Arthropods(the name means “jointed legs”) are
multicellular animals such as lobsters, shrimp, the
insects, ticks, and mites. Some insects (such as mos-
quitoes and fleas) are vectorsof disease; that is, they
spread pathogens from host to host when they bite to

obtain blood. Ticks are also vectors of certain diseases,

and some mites may cause infestations of the skin.

BINOMIAL NOMENCLATURE

We refer to bacteria and all other living things using

two names (binomial nomenclature), the genus and

the species. The genus name is placed first, is always

capitalized, and is the larger category. The species

name is second, is not capitalized, and is the smaller

category. Let us use as examples Staphylococcus aureus

and Staphylococcus epidermidis. These two bacteria are

in the same genus, Staphylococcus, which tells us that

they are related or similar to one another. Yet they are

different enough to be given their own species names:

aureusor epidermidis. It may be helpful here to think

of our own names. Each of us has a family name,

which indicates that we are related to other members

of our families, and each of us has a first name indi-

cating that we are individuals in this related group. If

we wrote our own names using the method of bino-

mial nomenclature, we would write Smith Mary and

Smith John.

In scientific articles and books, for the sake of con-

venience, the genus name is often abbreviated with its

first letter. We might read of S. aureusas a cause of a

food poisoning outbreak or see E. coli (E. for

An Introduction to Microbiology and Human Disease 499

BOX22–2 MICROBIOLOGY IN THE 20TH CENTURY

1962 The Sabin polio vaccine is marketed in the

United States.

1963 The measles vaccine becomes available.

1969 A vaccine for rubella is developed.

1976 Legionnaire’s disease is discovered and des-

cribed.

1980 Genetically engineered bacteria produce the

hormone insulin.

1981 The first cases of AIDS are described.

1982 The first vaccine for hepatitis B is licensed.

1986 Genetically engineered yeast are used to pro-

duce a more effective vaccine for hepatitis B.

Genetically engineered bacteria produce

human growth hormone.

1997 Avian flu H5N1 infects 18 people in Hong

Kong; then the virus seems to disappear until

2003.

1999 West Nile encephalitis virus is first reported in

North America, in New York City.

Just a few of the advances made in microbiology

during the 20th century are listed below. Many of

them concerned diagnosis, prevention, or treat-

ment of infectious diseases, and some involved

using microorganisms and the new genetic tech-

nologies.

1928 Discovery of penicillin by Alexander Fleming.

1935 The first of the sulfa drugs is found to be

effective against staphylococcal infections.

1938 Penicillin is purified and produced in large

quantities.

1941 The fluorescent antibody test is developed.

1943 Streptomycin is discovered and is the first

effective drug in the treatment of tuberculo-

sis.

1953 Watson and Crick describe the structure of

DNA.

1955 The Salk polio vaccine is first used.

1957 Interferon is discovered.

1959 A vaccine for whooping cough is available.