Chapter 7 microbiology

Filterable virus

An infectious agent small enough to pass through filters that trap bacteria; proved some diseases are caused by agents smaller than bacteria.

Cell-free filtered fluid

Fluid passed through a bacteria-trapping filter that still remained infectious.

Pasteur

Scientist who developed a vaccine for rabies.

Ivanovski

Scientist who showed in 1892 that tobacco mosaic disease was caused by a filterable infectious agent.

Beijerinck

Scientist who showed in 1898 that tobacco mosaic disease was caused by a virus.

Tobacco mosaic disease

A plant disease caused by a virus; important in early virus discovery.

Viruses

Infectious particles that are not cells and must use host cells to multiply.

Obligate intracellular parasites

Agents that cannot multiply unless they invade and use a specific host cell.

Virion

A fully formed virus particle capable of establishing infection in a host.

Capsid

The protein shell that surrounds the viral nucleic acid.

Envelope

A covering found in some viruses, usually made from a modified piece of the host cell membrane.

Spikes

Surface structures on naked or enveloped viruses that allow attachment to host cells.

Nucleic acid core

The genetic material inside a virus; viruses contain either DNA or RNA, but not both.

DNA viruses

Viruses that contain DNA as their genetic material and usually replicate in the nucleus.

RNA viruses

Viruses that contain RNA as their genetic material and usually replicate in the cytoplasm.

Viral genome

The genetic information of a virus; may be double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA.

Viral size range

Viruses are usually ultramicroscopic, ranging from about 20 nm to 1,500 nm.

What type of microscope is required to detect viral size range

Electron microscopes

Naked virus

A virus that has a capsid but no envelope.

Enveloped virus

A virus that has both a capsid and an envelope.

Complex capsid

A capsid with multiple protein types and a nonsymmetrical shape, often found in bacteriophages.

Bacteriophage

A virus that infects bacteria.

T-even bacteriophages

infect Escherichia coli.

Host range

The specific range of host cells a virus can infect based on matching host receptors.

Receptor site

A specific molecule on a host cell that a virus attaches to during infection.

Adsorption

The first step of viral infection, when a virus attaches to a host cell receptor.

Penetration

The entry of a virus or viral genetic material into a host cell.

Endocytosis

the entire virus is engulfed by the cell into a vesicle.

Uncoating

The removal or breakdown of the viral envelope and capsid, releasing viral genetic material.

Synthesis

The stage when viral nucleic acid takes control of the host cell to make viral parts.

Assembly

The stage when newly made viral components are put together into complete virions.

Release

The stage when newly formed viruses leave the host cell.

Budding

A release method used by enveloped viruses where the virus exits through the membrane and gains an envelope.

Exocytosis

A release method where viruses exit the host cell in vesicles.

Cytopathic effects

Visible virus-induced damage to host cells that changes their microscopic appearance.

Inclusion bodies

Compacted masses of viruses or damaged cell organelles in the nucleus or cytoplasm.

Syncytium

A large cell with multiple nuclei formed by the fusion of several host cells.

Persistent infection

A carrier relationship where a cell harbors a virus but is not immediately lysed.

Provirus

Viral DNA incorporated into the host cell’s DNA.

Chronic latent state

A state in which a virus remains inactive for a period and may later reactivate.

Latent viral infection

A viral infection where the virus remains in an asymptomatic host cell for a long time.

Cold sores

An example of a disease caused by reactivation of a latent virus.

Shingles

An example of a disease caused by reactivation of a latent virus.

Oncogenic virus

A virus capable of causing cancer.

Transformation

The process by which a virus causes a normal cell to become a tumor cell.

Oncogene

A gene that can transform normal cells into cancerous cells.

Viral taxonomy

The classification system used to organize viruses.

Viral genus

A virus classification level; genus names end in -virus.

Viral family

A virus classification level; family names end in -viridae.

Viral order

A virus classification level; order names end in -virales.

Viral species

A group of viruses sharing the same genetic information and ecological niche.

Subspecies

A lower virus classification designated by a number.

Lytic cycle

A bacteriophage life cycle that ends with destruction of the bacterial cell.

Lysogenic cycle

A bacteriophage life cycle where phage DNA becomes incorporated into host DNA.

Lysogeny

A silent viral infection where phage DNA remains latent in the bacterial chromosome.

Temperate phage

can enter a lysogenic cycle instead of immediately replicating and lysing the cell.

Prophage

Inactive phage DNA inserted into the host bacterial chromosome.

Induction

Activation of a prophage, causing it to enter viral replication and the lytic cycle.

Phage conversion

The process where a host cell gains new properties because it carries prophage DNA.

Lysogenic conversion

The acquisition of a new trait from a temperate phage.

Diphtheria toxin

A toxin whose production can result from lysogenic conversion.

Cholera toxin

A toxin whose production can result from lysogenic conversion.

Botulism toxin

production can result from lysogenic conversion.

Viral cultivation

Growing viruses in living hosts, embryos, or cell cultures for study or identification.

In vivo viral cultivation

Growing viruses in lab animals or embryonic bird tissues.

In vitro viral cultivation

Growing viruses in cell or tissue culture outside a living organism.

Lab animal inoculation

A method of cultivating viruses using specially bred animals such as mice, rats, hamsters, guinea pigs, or rabbits.

Bird embryo cultivation

A method of growing viruses in embryonic bird tissues inside a protective shell.

Cell culture

A method of growing isolated animal cells in sterile dishes or bottles to propagate viruses.

Tissue culture

Another term for cell culture used for in vitro virus cultivation.

Plaque

A clear, well-defined patch in a cell sheet caused by viral infection and lysis.

Plaque formation

The spread of viruses from an infected cell to nearby cells, producing a clear area in the culture.

Viral clinical specimens

Samples used to isolate and identify viruses in a medical setting.

Vaccines

Preparations that can be made using cultivated viruses to prevent viral disease.

Viral mutation

Rapid genetic change in viruses that makes treatment and vaccine design difficult.

Antibiotics

Drugs that are ineffective against viruses because viruses lack bacterial cell structures and processes.

Antiviral drugs

Drugs used against viruses, though relatively few are available.

Interferon

A naturally occurring human cell product used with some success to prevent and treat viral infections.

Acute viral infections

Common short-term viral infections such as colds, chickenpox, influenza, herpes, and warts.

Regional viral infections

Viral diseases that occur mainly in certain regions, such as dengue fever, Rift Valley fever, and yellow fever.

High-mortality viral infections

Viral infections with high death rates, such as rabies and Ebola.

Long-term disability viral infections

Viral infections that can cause lasting disability, such as polio and neonatal rubella.

Prions

Proteinaceous infectious particles that cause disease without nucleic acid.

Proteinaceous infectious particles

Infectious agents made of protein; another description of prions.

Spongiform encephalopathies

Prion-related diseases where affected brain tissue develops a sponge-like appearance.

Mad cow disease

A prion disease also called bovine spongiform encephalopathy.

Creutzfeldt-Jakob disease

A human prion disease affecting the central nervous system, causing degeneration and death.

Gerstmann-Sträussler-Scheinker syndrome

A prion disease listed among spongiform encephalopathies.

Fatal familial insomnia

A prion disease listed among spongiform encephalopathies.

Scrapie

A prion disease affecting sheep, mink, and elk.

Bovine spongiform encephalopathy

A prion disease affecting cows, also called mad cow disease.

Prion plaques

Deposits of abnormal protein fibrils that accumulate in brain cells.

How can prions be transmitted?

By ingestion, transplant, or surgical instruments.

Prion replication problem

The scientific question of how prions replicate even though they have no nucleic acid.

Viroids

Virus-like agents that infect plants and are made only of naked RNA.

Naked RNA

RNA without a capsid or other coating, found in viroids.

Viroid size

about one-tenth the size of an average virus.

Viroid plant diseases

Viroids are significant pathogens of tomatoes, potatoes, cucumbers, citrus trees, and chrysanthemums.

Viruses and evolution

Viruses have influenced host genetic makeup and helped shape the evolution of cells, tissues, bacteria, plants, and animals.

Human genome viral remnants

Between 40% and 80% of the human genome may be remnants of ancient viral infections.