Chapter 27

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 and tissues.

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 ...

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