Essentials of Anatomy and Physiology

An Introduction to Microbiology and Human Disease 525

4. Reservoirs—persons with the disease, carriers after
   recovery, or animal hosts (for zoonoses).


5. Noncommunicable disease—cannot be directly or
   indirectly transmitted from host to host.


6. Communicable disease—may be transmitted
   directly from host to host by respiratory droplets,
   cutaneous or sexual contact, placental transmission,
   or blood contact. May be transmitted indirectly by
   food or water, vectors, or fomites.


7. Contagious disease—easily spread from person to
   person by casual cutaneous contact or respiratory
   droplets.

Methods of Control of Microbes

1. Antiseptics—chemicals that destroy or inhibit bac-
   teria on a living being.


2. Disinfectants—chemicals that destroy or inhibit
   bacteria on inanimate objects.


3. Sterilization—a process that destroys all living
   organisms.


4. Public health measures include laws and regula-
   tions to ensure safe food and water.

Bacteria—see Fig. 22–2

1. Shapes: coccus, bacillus, and spirillum.


2. Flagella provide motility for some bacilli and spir-
   illa.


3. Aerobes require oxygen; anaerobes are inhibited by
   oxygen; facultative anaerobes grow in the presence
   or absence of oxygen.


4. The gram reaction (positive or negative) is based
   on the chemistry of the cell wall. The Gram stain is
   a laboratory procedure used in the identification of
   bacteria.


5. Capsules inhibit phagocytosis by white blood cells.
   Spores are dormant forms that are resistant to envi-
   ronmental extremes.


6. Toxins are chemicals produced by bacteria that are
   poisonous to host cells.


7. Rickettsias and chlamydias differ from other bacte-
   ria in that they must be inside living cells to repro-
   duce.


8. Antibiotics are chemicals used in the treatment of
   bacterial diseases. Broad-spectrum: affects many
   kinds of bacteria. Narrow-spectrum: affects only a
   few kinds of bacteria.


9. Bacteria may become resistant to certain antibi-
   otics, which are then of no use in treatment.
   Resistance is a genetic trait, and will be passed to

future generations. Culture and sensitivity testing

may be necessary before an antibiotic is chosen to

treat an infection.

10. Diseases—see Table 22–3.

Viruses—see Fig. 22–3

1. Not cells; a virus consists of either DNA or RNA
   surrounded by a protein shell.


2. Must be inside living cells to reproduce, which
   causes death of the host cell.


3. Severity of disease depends on the types of cells
   infected; some viruses may cross the placenta and
   infect a fetus.


4. Antiviral medications must interfere with viral
   reproduction without harming host cells.


5. Diseases—see Table 22–4.

Fungi—see Fig. 22–4

1. Most are saprophytes, decomposers of dead
   organic matter. May be unicellular yeasts or multi-
   cellular molds.


2. Mycoses may be superficial, involving the skin or
   mucous membranes, or systemic, involving internal
   organs such as the lungs or meninges.


3. Effective antifungal medications are available, but
   some are highly toxic.


4. Diseases—see Table 22–5.

Protozoa—see Fig. 22–5

1. Unicellular animals; some are pathogens.


2. Some are spread by vectors, others by fecal con-
   tamination of food or water.


3. Effective medications are available for most dis-
   eases.


4. Diseases—see Table 22–6.

Worms—see Fig. 22–6

1. Simple multicellular animals; the parasites are
   flukes, tapeworms, and some roundworms.


2. May have life cycles that involve other animal hosts
   as well as people.


3. Effective medications are available for most worm
   infestations.


4. Diseases—see Table 22–7.

Arthropods—see Fig. 22–7

1. Some cause superficial infestations.


2. Others are vectors of disease—see Table 22–8.