F

Facultative: A qualifying adjective used to indicate that an organisms is able to grow in either the presence or absence of such an environmental factor as oxygen. Facultative anaerobes can grow with, or without, air.
Falciparum malaria: The most dangerous form of malaria caused by Plasmodium falciparum. It is often resistant to treatment with common anti-malarial drugs.
Fasciitis, necrotizing: An invasive infection of the tissues and muscle that spreads along the connective tissues, separating muscle groups (fascia), leading to tissue death.
Fastidious: A cell requires special nutrient supplementation in order to grow.
Fermentation: The anaerobic breakdown of organic compounds, especially carbohydrates, to simpler compounds.
Fever: The above normal body temperature of 37°C (98.6°F). What causes fever? The thermal regulatory center in the brain controls body temperature. The brain's temperature setting rises during an infection because the white blood cells release certain proteins during an immune response. These proteins trigger the brain to release a chemical called prostaglandins, which cause the nerve cells to produce sensations of coldness. This is why chills usually go along with a fever. In response to coldness, the brain increases the body temperature, which in turn speeds up the activities of the immune system against germs. Fevers are not usually harmful, and actually fight infections. To stop a fever allows the germs to multiply; therefore, fevers are an important defence mechanism. Prolonged fevers over 39°C (102°F) should be reported, however. An infant younger than three months that has a fever over 38°C (100.4°F) should be investigated. The degree of a fever is not an indicator of the seriousness of an illness. Severe infections can spark a low body temperature, while a mild infection can produce a high temperature.
Filamentous: The formation of rods that are many times longer than they are wide.
Filaria: Micropscopic parasitic roundworms (Filaria) transmitted by the bite of mosquitoes.
Filoviruses: Filamentous viruses tentatively classified in the family Filoviridae. Two have been identified so far: the Marburg virus, with a mortality rate of 25%, and Ebola with a mortality rate of 90%.
Fimbria (plural fimbriae): A short filamentous structure on a bacterial cell. Although flagella-like in structure, it is not involved in motility, instead, playing a role in adherence to surfaces and in the formation of pellicles (see also pilus).
Flagellum (plural flagella): An organ of motility. The rotation of some flagella has been measured at over 2,000 rpm, causing some to move ten times the length of their cell in one second. Certain bacteria have only a single flagellum and are called monotrichous (trichous means hair-like). Some have tufts of flagella and are called lophotrichous. Others have flagella protruding from all areas of the cell and are called peritrichous.
Flatworms: A group of worms that include flukes, tapeworms, and schistosomes, as well as free-living forms like the planaria.
Flaviviruses: Arthropod-borne viruses that belong to the family Togaviridae producing such diseases as Zika fever.
Flukes: An organism of the class Trematoda that include several species of leaf-shaped parasitic flatworms that inhabit the lungs, liver, intestines, and bladder.
Fluorescent Antibody test (FAT): A test to reveal antibodies through the use of fluorescent lighting.
Formalin: A solution of formaldehyde used for preserving tissue for study.
Fomites: Inanimate objects that act as vectors in the spread of an infection.
Food poisoning: An illness that results from the presence of toxins, usually from a viral or bacterial source, that contaminate a food source.
Fulminating: The running of a rapid course of infection with a continued worsening of a condition.
Fundi: Structures forming the back wall of the eye (retina and its blood vessels), seen only with an ophthalmoscope.
Fungaemia: The presence of fungi in the bloodstream.
Fungi (singular fungus): Eukaryotic organisms that reproduce with spores and lack the ability to create food with light. Fungi include such diverse organisms as yeasts, molds, and mushrooms. Larger than bacteria, fungi are usually endowed with a nearly invisible network of root-like threads and large fruiting bodies (eg. mushrooms). Yeasts do not contain the branching threads, but, instead, are globular-shaped cells that multiply by budding. Molds consist of masses of branchlike filaments called hyphae. Reproduction results in the formation of large numbers of seedlike structures called spores. The most notable function of fungi is their ability to secrete powerful enzymes that decompose organic matter.
Fungicide: Anything that kills fungi.
Furuncle: A boil resulting from a Staphylococcus aureus infection of a single hair follicle.