Section V

Vaccination: Artificial introduction of a killed or attenuated pathogen to promote protective immunity. See vaccine.

Vaccine: Material used to induce specific protective immunity against a pathogen.

Vacuole: Cavity in the cytoplasm of a cell that may contain ingested bacteria, yeast cells, or debris; vacuole contents and/or morphology may be helpful in identification of some of the intestinal protozoa (Entamoeba spp., lodamoeba butschlii).

Vaginitis: Inflammation of the vagina; prolific, irritating green or yellowish, thin discharge; there may be punctate, hemorrhagic spots (trichomoniasis).

Vancomycin: An antibiotic used in the presumptive identification of anaerobic bacteria. Anaerobic gram-negative organisms (except Porphyromonas spp.) are resistant to this antibiotic.

Vasculitis: Inflammation of blood vessels leading to lesions leading to lesions on the skin, mucous membranes.

VD: Venereal disease.

VDRL: Venereal Disease Research Laboratory; classic nontreponemal serologic test for syphilis antibodies. Uses cardiolipin, lecithin, and cholesterol as cross-reactive antigen that flocculates in the presence of "reaginic" antibodies produced by patients with syphilis. Best test for cerebrospinal fluid in cases of neurosyphilis.

Vector: 1. A plasmid or virus used in genetic engineering to insert genes into a cell. 2. An agent, usually an insect or other animal, able to carry pathogens from one host to another. 3.An arthropod or other agent that carries microorganisms from one infected individual to another.

Vegetation: In endocarditis, the aggregates of fibrin and microorganisms on the heart valves or other endocardium.

Vehicle: Nonliving source of pathogens which infect large numbers of individuals; common vehicles are food and water.

Venipuncture: A procedure used to draw blood or inject a solution that involves puncturing a vein.

Verrucose: Surface with wartlike projections.

Vertical transmission: Passage of an infectious agent form the mother to an unborn child.

Verticillate: With branches arranged in verticils or whorls.

Vesicle¹: Enlarged structure at the end of a coniodiophore or sporangiophore. In Aspergillus spp. it bears the phialides, which in turn bear the conidia.

Vesicle²: A small bulla or blister containing clear fluid.

Vesiculopustular: Pertaining to blisterlike lesions containing pus.

Viable: Alive; able to reproduce.

Viable count: Measurement of the concentration of live cells in a microbial population.

Vibrio¹: A curved, rod-shaped bacterial cell.

Vibrio²: A bacterium of the genus Vibrio.

Vibrioid: Curved in three dimensions but having less than one complete turn.

Villi: Minute, elongated projections from the surface of intestinal mucosa that are important in absorption.

Vincent angina: An old term, seldom used presently, referring to anaerobic tonsillitis.

Vinegar eel: Free-living nematode, Turbatrix aceti, occasionally occurring as a contaminant in laboratory solutions.

Viremia: Presence of viruses in the bloodstream.

Virion: The whole viral particle, including nucleocapsid, outer membrane or envelope and all adherence structures.

Viroid: A small RNA molecule with virus-like properties.

Virulence: Degree of pathogenicity or disease-producing ability of a microorganism.

Virus: A genetic element containing either DNA or RNA that is able to alternate between intracellular and extracellular states, the latter being the infectious state.

Visceral: Pertaining to the internal organs of the body, especially those within the abdominal cavity.

Visceral larva migrans: Tissue migration of dog and cat ascarid larvae in humans; the life cycle cannot be completed in the human host; often characterized by high peripheral eosinophilia (Toxocara cati and T. canis).

Viscus (pl., viscera): Any of the organs within one of the four great body cavities (cranium, thorax, abdomen, and pelvis).

Vitamin: Any organic compound which is necessary for the normal metabolism and growth of microorganisms. A vitamin typically functions as a coenzyme or a component of a coenzyme and is required by microorganisms in small quantities. All microorganisms require some vitamins of different varieties; they can either synthesize vitamins by themselves or they have to obtain them from the growth medium. Examples of some important vitamins are: nicotinic acid, riboflavin, pantothenic acid, biotin, PABA, thiamine, B12, folic acid, etc.

Vitamin C: Ascorbic acid, an anti-oxidant, protecting organisms from oxidative damage.

Vitamin E: An anti-oxidant, protecting organisms from oxidative damage. Occurs in wheat germ oil, cereals, beef liver, and egg yolk.

V-P: Voges-Proskauer.

VVC: Vulvovaginal candidiasis.

VZV: Varicella-zoster virus.

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