DRUGS USED TO PREVENT AND TREAT INFECTION I
Section I. MICROBIOLOGY
Bacteria are minute, single-celled living organisms of the kingdom Protista, which
exist on either living or dead hosts. While there are many hundred individual species of
bacteria, only a few of them are capable of producing disease in man. Disease-
producing organisms are termed pathogens; they are said to be pathogenic.
a. Morphology. Morphology is the study of the forms and structures of
organized beings. Bacteria can be broken down into three broad groups based on their
general shape. There are the spherical bacteria called cocci (coccus, singular); the rod-
shaped bacteria called bacilli (bacillus, singular); and the spiral-shaped bacteria called
(1) Cocci. Cocci (spherical bacteria) may be arranged in pairs, chains, or
clusters. Depending upon their arrangement, they are called diplococci (pairs),
streptococci (chains), or staphylococci (clusters).
Bacilli. The rod-shaped bacilli occur singly, in pairs, or in chains.
Spirochetes. Spiral-shaped bacteria always occur singly.
b. Locomotion (Motility). Since most bacteria have no special structure for
locomotion, they lack the ability to move by themselves. They are carried along with the
movement of food in the digestive tract or blood in the vessels. A very few of the
pathogens are equipped with one or more hairlike projections called flagella. These
flagella permit the organism to propel itself by whiplike motions.
c. Capsules. Certain bacteria can cover themselves with a gelatinous
substance. This covering is called a capsule and the process is termed encapsulation.
It serves to protect the organism from adverse conditions such as heat, cold, moisture,
drying, or drug therapy. Encapsulated organisms are immune to the process of
phagocytosis, a defensive body mechanism in which bacteria are engulfed by certain
white blood cells.
d. Size. Bacteria are microscopic in size. Their size is usually expressed in
units of microns; one micron is 1/1000 mm (1/25,400 inch). Most bacteria are from 0.5
to 2.0 microns in size.