Infectious diseases are among the most common forms of illness.
Thus, many patients undergoing physical rehabilitation may be taking
one or more antimicrobial drugs. Most agents (but not all) have
little direct impact on the functional rehabilitation outcomes,
but they will certainly have an impact on the overall health status
of the patient.
The next four chapters address agents used to treat infections
caused by various parasites including bacteria, viruses, fungi,
protozoa, and helminths (worms). Once these pathogens gain access
inside the human body, they can cause illnesses ranging from minor
infections to life-threatening illnesses. Antimicrobial drugs are among
the most dramatic examples of advances of modern medicine; many
infectious diseases once considered incurable and lethal are now
amenable to treatment. Antimicrobial drugs are classified and identified
according to the primary type of infectious organism they are used
to treat (e.g., antibacterial, antiviral, antifungal).
The remarkably powerful and specific activity of antimicrobial
drugs is due to selective toxicity—that
is, drugs are designed to target structures selectively that are
either unique to microorganisms or much more important in them than
in humans. Therefore, a general understanding of microbial structure
and function is necessary to understand the mechanisms of action
of antimicrobial agents. Notably, selective toxicity is not perfect,
and antimicrobials may exert some adverse effects in humans.
Bacterial infections harm humans in several ways. Bacteria can
directly damage or destroy human cells by releasing toxins, and
they can compete with human cells for vital nutrients. In addition,
in immunocompetent individuals, bacteria trigger a host immune response
that may damage not only pathogenic bacteria but also human cells
It is also important to understand that not all bacteria living
in the human body are harmful. In fact, some bacteria normally coexist
within humans and actually benefit their human hosts. For example, Escherichia coli microorganisms normally inhabit the gastrointestinal
tract and are thus considered part of the normal flora. E coli assist in digestion of food,
synthesize essential nutrients such as vitamin K, and inhibit the growth
of other organisms. As an illustration of the latter function, antibiotic
therapy often results in the eradication of normal gut flora. After
antibiotic treatment is completed, overgrowth of other microorganisms
(e.g., yeasts) often occurs.
The target site for antibacterial drugs, or antibiotics, is either
the cell wall or structures involved in bacterial reproduction.
Bacteria are single-celled prokaryotes (cells
without a distinct nucleus) that have a characteristic cellular
organization. Fungi, protozoa, and multicellular organisms have
nuclei containing their genetic material and are called eukaryotes. Viruses, on the other
hand, are not strictly cellular at all and comprise a very different
form of life. Bacterial deoxyribonucleic acid (DNA) forms a long
circular molecule called a nucleoid. In addition, genetic information
may be present in DNA molecules termed plasmids.
Plasmids replicate independently of chromosomal DNA and may carry
genes that affect ...