Chapter 40.6, Problem 3CC

Summary Introduction

An opportunistic organism is one that is generally harmless in its normal environment but can become pathogenic in a compromised host. It becomes pathogenic when (1) introduced to a new environment, (2) outcompetes the other resident microbes, or (3) the host becomes (immuno-) compromised. A compromised host is seriously debilitated and has lowered resistance to infection. There are many causes of this condition: malnutrition, alcoholism, cancer, diabetes, another infectious disease (e.g., HIV/AIDS), trauma from surgery or injury, an altered microbiota from prolonged use of antibiotics (e.g., in vaginal candidiasis), and immunosuppression (e.g., by drugs, hormones, genetic deficiencies, cancer chemotherapy, and old age). Opportunistic mycoses may start as normal microbiota or ubiquitous environmental contaminants. An emerging opportunistic fungal disease, especially of the immunocompromised, is caused by the group of unique microbes known as the microsporidia. They live as a spore form and have a unique organelle used for infecting new host cells.