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.