Of the approximately 70,000 recognized species of fungi, about 300 are known to cause human infections. In addition, some fungi have economic importance as plant and animal pathogens. Fungal diseases of healthy humans tend to be relatively benign, but the few life-threatening fungal diseases are extremely important. Fungal diseases are an increasing problem due to the use of antibacterial and immunosuppressive agents. Individuals with an altered bacterial flora or compromised defense mechanisms (e.g., AIDS patients) are more likely than healthy people to develop opportunistic fungal infections such as candidiasis. Consequently, opportunistic fungal pathogens are increasingly important in medical microbiology.
Fungi are eukaryotes. They possess a nucleus enclosed by a nuclear membrane, a rigid cell wall, endoplasmic reticulum, and mitochondria like those of plant and animal cells. These structures differ substantially from those of bacteria. Host defenses against fungi are similar to those utilized against bacterial diseases, except that the cell-mediated response is extremely important. Nonspecific immunity and cell-mediated immunity seem to be the most important means by which humans resist or eliminate fungal pathogens. It is the purpose of this section to provide a basic understanding of fungi and the diseases they cause.
Michael R. McGinnis