F : Fluorimetry.

^o F : Fahrenheit.

FA : Fluorescent antibody.

Facultative : Literally means "optional"; an adjective used to describe that an environmental factor is optionally (not necessarily) required for an organism to grow. For example, a facultative anaerobe can normally grow in the presence of oxygen but alternatively, it can also grow without oxygen.

Facultative aerobe : An organism which is normally anaerobic but can also grow in the presence or oxygen (O2).

Facultative anaerobe : An organism that can grow well both in the absence of oxygen and in the presence of a level of oxygen equivalent to that in an air atmosphere (21%). Some are capable of growing aerobically by respiring with oxygen and of growing anaerobically by fermentation; others have a strictly fermentative type of metabolism and do not respire with oxygen.

Fascia : Membranous covering of muscle.

Favic chandeliers : Terminal hyphal branches that are irregular, broad, and antler-like in appearance. Especially characteristic of Trichophyton schoenleini.

Favus : Dermatophyte infection of the scalp produced by Trichophyton schoenleinii.

FC : Flow cyctometry.

FDA : Food and Drug Administration.

Febrile : Relating to fever.

Feces : The unabsorbed residue of the digestive process, along with sloughed epithelium, mucus, and bacteria.

Feedback inhibition : Inhibition by an end product of the biosynthetic pathway involved in its synthesis.

Fermentation : An energy-yielding metabolic process in which electrons derived from an organic substrate are used ultimately to reduce an organic electron acceptor that is made by the cell itself. Neither an electron transport chain nor an exogenous terminal electron acceptor is involved. (Contrast with respiration).

Fermenter : An organism which carries out the process of fermentation.

Fermentor : A large growth vessel used to culture microorganisms on a large scale, frequently for the production of some commercially valuable product.

Ferredoxin : An electron carrier of low reduction potential; small protein containing iron-sulfur clusters.

FeCl3 : Ferric chloride.

Fever : A rise of body temperature above the normal.

Filamentous : Long, cylindrical, and threadlike; hyphae forming.

Filariform larvae : Slender, infective larvae of Strongyloides stercoralis and hookworm.

Fimbriae : Proteinaceous fingerlike surface structures of bacteria that provide for adherence to host surfaces.

Fission : Division of a cell into two cells by splitting.

Fistula : Abnormal communication between two surfaces or between a viscus or other hollow structure and the exterior.

Fitz-Hugh-Curtis syndrome : Inflammation of the capsule of the liver that may be seen in course of gonococcal or chlamydial infection in the female.

Flagellum (plural flagella) : An organ of motility; composed of tightly wound chains of strands containing a protein called flagellin.

Flame cell : Primitive, ciliated excretory cell in trematodes; the movement of the cilia on this cell within the miracidium larva (within a schistosome egg) indicates egg viability.

Flatulence : The presence of excessive gas in the stomach and intestines.

Flavin : An enzyme that contains, as tightly bound prosthetic groups, either flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD).

Flavoprotein : A protein containing a derivative of riboflavin, which acts as electron carrier in the electron-transport system.

Flesh-eating bacteria : A strain of Group A streptococcus which, in severe cases, can destroy tissue as fast as surgeons can cut it out. The rapid destruction of tissue caused by these bacteria is localized, so it is unlikely to be caused by a general over stimulation of the immune system by, for example, superantigen exotoxin A. Instead, the invasive strains of strep A probably have other toxin(s) such as exotoxin B, an enzyme (i.e. cysteine protease) that destroys tissue by breaking down protein. (Ref: Science 264:1665, 1994).

FLO : Flocculation.

Floccose : Cottony; like raw, fuzzy cotton.

Flocculation test : Antigen-antibody test in which a precipitin end product forms macroscopically or microscopically visible clumps.

Flow Cytometry (FC) , is an emerging technique which holds great promise for the separation, classification and quantitation of blood cells and antibodies which affect blood cells. Complex computerized instruments are used to pass a monocellular stream of cells, platelets or other microscopic particulate elements through a beam of laser light. The cells are categorized first by size and then computer analyzed to sort the mixture of cellular elements into cell type by size. In addition, monoclonal antibodies to specific cell surface markers are conjugated to fluorescent dyes and each cell displaying appropriate fluorescent light emission is counted. Tabulation of counted data in conjunction with size analysis enables determination of relative percentages of each specific cellular subset for which monoclonal conjugates are utilized, even when the size of the cell is identical to other subset species.

Fluke : Trematode (Clonorchis, Paragonimus, Fasciola, and Schistosoma spp.).

Fluorescence Polarization Immunoassay (FPIA) , is a technique which takes advantage of the increased polarization (non-random propagation of emission) of fluorescent light emissions when a fluorescently labeled antigen is bound by reagent antibody. The higher the concentration of unlabeled patient antigen present in the test mixture, the less bound fluorescent antigen is present and, consequently, the lower the polarization of the fluorescent light emission. Standard calibration yields quantitative results.

Fluorescent antibody : Immunoglobulin molecule which as been coupled with a fluorescent molecule so that it exhibits fluorescence.

Fluorescent Antibody (FA) , assay is a general term for procedures which utilize the visual detection of fluorescent dyes coupled (conjugated) to antibodies which react with the antigen when present using fluorescent microscopy. FA allows a competent technologist to identify visually the site of the antigen-antibody reaction thereby rendering significant specificity. Variations are further explained below (DFA, IFA, ACIF, ABIF, and Microif).

Fluorescent immunoassays (FIAs) : Similar to RIA by employ fluorescent molecules as labels.

Fluorescent : Emission of light by a substance (or a microscopic preparation) while acted on by radiant energy, such as ultraviolet rays, as in the immunofluorescent procedure.

Fluorochrome : A dye that becomes fluorescent or self-luminous after exposure to ultraviolet light.

Fomite : Any inanimate object that may be contaminated with disease-causing microorganisms and thus serves to transmit disease.

Fontanelles : Soft area between the cranial bones of an infant's skull, indicative of areas not yet ossified.

Food infection : Microbial infection resulting from ingestion of contaminated food.

Food irradiation : A technology that provides a specific dose of ionizing radiation from a source such as a radioisotope (e.g., Cobalt 60), or from machines that produce accelerated electron beams or x-rays. Doses for irradiation of food and material are: low, 1 or less kiloGrays (kGy), used for disinfestation of insects from fruit, spices and grain; and parasite disinfection from fish and meat; medium, 1-10 kGy (commonly 1-4kGy), used for pasteurization and the destruction of bacteria and fungi; and high, 10-50 kGy, used for sterilization of food as well as medical supplies (including IV fluids, implants, syringes, needles, thread, clips and gowns).

Food poisoning : Disease resulting from ingestion of food contaminated with a toxin produced by a microorganism.

Foot cell : The base of the conidiophore, where it merges with the hyphae, giving the impression of a foot; typically seen in Aspergillus spp.

FPIA : Fluorescence polarization immunoassay.

Fragmentation : Breaking of the hyphae into pieces, each of which is capable of forming a new organism. Arthroconidia are formed in this manner.

Free energy : Energy available to do useful work.

Fruiting Body : A specialized macroscopic, spore-producing structure that is composed of slime and bacterial cells, is often brightly colored, and may be visible to the naked eye. Formed by some fungi (e.g., mushrooms) and Mycobacteria. Fruiting bodies are distinct in size, shape, and coloration for each species.

FTA : Fluorescent treponemal antibody.

FTA-ABS : Fluorescent Treponemal Antigen-Antibody absorption test; indirect fluorescent antibody stain used to detect antibodies directed against whole cell antigens of Treponema pallidum (syphilis bacillus).

Fulminant : The sudden occurrence of an intense or severe process.

Fumigation : Any process by which the killing of animal forms, especially arthropods and rodents, is accomplished by the use of gaseous agents. (See Insecticide and Rodenticide).

Fungemia : Presence of viable fungi in blood.

Fungus (pl. fungi) : An organism that is either filamentous or unicellular and lacks chlorophyll. It has a true nucleus enclosed in a membrane and chitin in the cell wall.

Funiculitis : Inflammation of the spermatic cord (filariasis).

FUO : Fever of unknown origin.

Fuseau : A fusiform or spindle-shaped, multiseptate macroconidium.

Fusiform : Spindle shaped (i.e. being wider in the middle and narrowing toward the ends).

Fusion protein : The result of translation of two or more genes joined such that they retain their correct reading frames but make a single protein.