from chitin, which is a unique property of fungal organisms. Single-celled fungi are typically yeast organisms, of which there are at least a thousand species known. They live in many different environments; only a few are considered pathogenic to humans and animals. Molds are multicellular fungal organisms that form colonies that can be seen by the human eye. You can see molds in damp environments, such as bathrooms and rotting plants. Molds participate in the decompensation process and are known allergens to humans. Some molds make mycotoxins that cause diseases. Molds can be helpful too, particularly in the making of certain antibiotics, including penicillin. Helminths are multicellular pathogens and are visible with the naked eye. The are not truly microorganisms but they do have microscopic larvae and eggs. There are multiple types of helminths that cause disease, such as tapeworms and pinworms, which reside in the gastrointestinal system. Viruses are acellular so they do not technically qualify as living things. Viruses are basically genetic material covered in a protein coat and sometimes wrapped in an envelope. They do not function independently but must incorporate their genetic material into a host cell in order to replicate their genome. There are viruses that infect bacteria, called bacteriophages, and viruses that attack other types of organisms. Surprisingly, not all viruses are strictly pathogenic.
FUNDAMENTALS OF MICROSCOPY As you will learn in this section, there are several different types of microscopy. The concept of invisible species being the cause of disease was first developed in the 1500s. At the time, there were no scientific techniques for actually seeing them, however. The first microscope was made by Antonie van Leeuwenhoek, who is believed to be the “father of microbiology”. He first observed single-celled organisms in the late 1600s. Galileo also pioneered the field of microscopy. Galileo used a compound microscope to evaluate insects, while van Leeuwenhoek developed light microscopy that could see bacteria.
8
