e. Reproduction. Bacteria reproduce rapidly, about once every 30 minutes,
through a process called binary fission. Each bacterium splits into two new organisms
in this reproductive process. Under ideal conditions, a single bacterium could produce a
total of 140,000,000,000,000 organisms in a period of 24 hours. Of course, conditions
are never ideal. A limited food supply diminishes bacterial reproduction.
f. Classification. One way by which bacteria may be classified is by the
manner in which they are stained by certain dyes. In this classification, most bacteria
are divided into two broad groups, the gram-positive and the gram-negative bacteria.
Slides are treated with a crystal violet stain followed by safranine stain. Gram-positive
organisms (G+) become purple-colored because of the crystal violet. Gram-negative
(G-) organisms are stained red by the safranine.
g. Relationship to Disease. Many diseases are wholly or partly a result of the
presence of bacteria in the blood or tissues. The pathogenic effects of some of these
bacteria result from the toxins they produce.
h. Common Bacterial Diseases. Streptococci, staphylococci, and
pneumococci--all gram-positive organisms--are responsible for 80 percent to 90 percent
of all clinical bacterial infections. The streptococcus is responsible for bacterial
endocarditis, strep throat, and scarlet fever. The staphylococcus causes boils and other
miscellaneous infections. The pneumococcus causes pneumonia. Various gram-
negative bacteria are responsible for peritonitis, urinary tract infections, gonorrhea,
whooping cough, plague, and wound infections.
i. General Drug Treatment. Most bacterial infections respond well to
treatment with sulfonamides or antibiotics.
The virus is an infectious agent, submicroscopic in size, that is capable of
multiplication only within a living cell. Because of their extremely small size, relatively
little is known about viruses.
a. Morphology. There is little uniformity among the viruses. They may be
ovoid, spherical, rodlike, or tadpole-shaped.
b. Locomotion (Motility). None of the viruses yet studied possess a
mechanism for independent movement.
c. Size. Viruses are much smaller than bacteria. They are measured in
millimicrons (1/1000th micron). An electron microscope with a magnification of 100,000
times is necessary to see an average virus. Such magnification would make a mosquito
appear as large as the Empire State Building!