Essentials of Anatomy and Physiology

An Introduction to Microbiology and Human Disease 509

G

I

H

J

A

D

B

E

C

F

Spirillum

Bacterial spores

Bacillus

E Flagella

Coccus

Bacterial capsules

Figure 22–2. (A–F) Bacterial
shapes and specialized structures
(magnification x 2000) (G) Gram-
positive Staphylococcus aureus (x
1000). (H) Gram-negative Neisseria
gonorrhoeaein WBCs (x 1000). (I)
Gram-negativeCampylobacter jejuni
(x 1000). (J)Salmonella enteritidis
growing on agar in a Petri dish. The
black colonies indicate production
of hydrogen sulfide gas. (G–J from
Sacher, RA, and McPherson, RA:
Widmann’s Clinical Interpretation of
Laboratory Tests. ed 11, FA Davis,
Philadelphia, 2000, color plates 58,
59, 60 and 92, with permission.)
QUESTION:In parts A–F, most of
the bacteria are blue or pink. What
do these colors indicate? The spiril-
lum, C, is neither color. What does
this tell us?

digestive enzymes, which break down the food we eat.
Some bacterial toxins such as hemolysins and pro-
teases literally digest host tissues such as red blood
cells and proteins. The bacteria then absorb the
digested nutrients.
The toxins of other bacteria have very specific
effects on certain cells of the host. Botulism and
tetanus toxins, for example, are neurotoxins that
disrupt the functioning of nerve cells, leading to the
characteristic symptoms of each disease. The diph-
theria toxin causes heart failure, the pertussis (whoop-
ing cough) toxin immobilizes the cilia of the
respiratory tract, and the cholera enterotoxin causes
diarrhea.

The cell walls of gram-negative bacteria are made

of chemicals called endotoxins. Endotoxinsall have

the same effects on the host: They cause fever and cir-

culatory shock (low blood pressure and heart failure).

Endotoxin shock(also called gram-negative shock)

is a life-threatening condition that may accompany

any serious infection with gram-negative bacteria.

Rickettsias and Chlamydias

These two groups of bacteria differ from most other

bacteria in that they are obligate intracellular para-

sites. This means that they can reproduce only within

the living cells of a host.