Microbiology Chapter #13

• Obligatory intracellular parasites
• Contain DNA or RNA
• Contain a protein coat
• Some are enclosed by an envelope
• Some viruses have spikes
• Most viruses infect only specific types of cells in one host
• Host range is determined by specific host attachment sites and cellular factors

• No plasma membrane
• Do not reproduce by binary fission
• Don’t possess DNA and RNA simultaneously
• No ribosomes
• Don’t make ATP
• Are not sensitive to antibiotics
• Contain few or no enzymes of their own

Host range (Host range is specific )

Specific types of cells in specific hosts

Bacteriophages (phages)

Viron.

DNA or RNA

• Enveloped
• Helical
• Polyhedral

• Long rods
• Nucleic acid in a hollow cylindrical capsid
• Rabies virus
• Ebola virus

• Many-sided viruses
• Many plant and animal viruses of this type
• Icosahedron
• Adenovirus
• Polio virus

Bacterial viruses - Contain complex structures for transfer of DNA to host cell

• Nucleic acid type
• Strategy for replication
• Morphology
• The suffix “-ales” is used for orders
• The suffix “-viradae” is used for families
• The suffix “-virus” is used as a genus name
• Common names are used for species.
• Subspecies are designated by a number.

Viral species

• Herpesviridae
• Herpesvirus
• Human herpes virus HHV-1, HHV-2, HHV-3
• Retroviridae
• Lentivirus
• Human immunodeficiency virus HIV-1, HIV-2

Viruses must be grown in living cells

Bacteriophages

Animal viruses may be grown in living animals or in embryonated eggs

Animal and plant viruses may be grown in cell culture. Continuous cell lines may be maintained indefinitely

• Cytopathic effects
• Serological tests
• Nucleic acids ( Rflps, PCR)

Serological tests

• Attachment: Phage attaches by tail fibers to host cell
• Penetration: Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell
• Biosynthesis: Production of phage DNA and proteins
• Maturation: Assembly of phage particles
• Release: Phage lysozyme breaks cell wall

• Attachment: Viruses attach to cell membrane
• Penetration: by endocytosis or fusion
• Uncoating: by viral or host enzymes
• Biosynthesis: Production of nucleic acid and proteins
• Maturation: Nucleic acid and capsid proteins assemble
• Release: by budding (enveloped viruses) or rupture

• DNA replicated in the nucleus and the capsid is replicated in the cytoplasm.
• Capsid proteins then migrate to the nucleus.
• Virons are formed in the nucleus.
• Virons transported along Endoplasmic reticulum to the plasma membrane for release.

• Parvovirdae
• Adenovirdae
• Poxvirdae
• Herpesviridae
• Papovavirdae
• Hepadnavirdae

• Single-stranded DNA, nonenveloped viruses,
• Fifth disease
• Anemia in immunocompromised patients

• Double-stranded DNA, nonenveloped viruses
• Respiratory infections in humans
• Tumors in animals

• Double-stranded DNA, enveloped viruses
• Orthopoxvirus (vaccinia and smallpox viruses)
• Molluscipoxvirus
• Smallpox
• Molluscum contagiosum
• Cowpox

• Double-stranded DNA, enveloped viruses
• Simplexvirus (HHV-1 and HHV-2)
• Varicellovirus (HHV-3)
• Lymphocryptovirus (HHV-4)
• Cytomegalovirus (HHV-5)
• Roseolovirus (HHV-6)
• HHV-7
• Kaposi's sarcoma (HHV-8)
• Some herpesviruses can remain latent in host cells

Double-stranded DNA, nonenveloped viruses

Human wart virus

Cause tumors; some cause cancer

• Double-stranded DNA, enveloped viruses
• Hepatitis B virus
• Use reverse transcriptase

• Picornavirdae
• Togaviridae
• Rhabodoviridae
• Caliciviridae
• Reoviridae
• Retroviridae

• Single-stranded RNA, + strand, nonenveloped
• Enterovirus: Poliovirus and coxsackievirus
• Rhinovirus
• Hepatitis A virus

• Single-stranded RNA, + strand, enveloped
• Alphavirus :Transmitted by arthropods; includes EEE and WEE
• Rubivirus (rubella virus)

• Single-stranded RNA, – strand, one RNA strand
• Vesiculovirus
• Lyssavirus (rabies virus)
• Cause numerous animal diseases

• Single-stranded RNA, + strand, nonenveloped
• Hepatitis E virus
• Norovirus causes gastroenteritis

• Double-stranded RNA, nonenveloped
• Reovirus (respiratory enteric orphan)
• Rotavirus (mild respiratory infections and gastroenteritis)
• Colorado tick fever

• Single-stranded RNA, 2 RNA strands,
• produce DNA
• Use reverse transcriptase to produce DNA from viral genome
• Lentivirus (HIV)
• Oncogenic viruses
• Includes all RNA tumor viruses

• Several cancers are known to be caused by viruses
• Often go un-noticed
• Most viruses do not cause cancer
• Cancer takes a long time to develop
• Cancer is not contagious like viruses
• Viruses cause cancers by activating oncogenes
• Only 10% of cancers have been liked to viruses

• Transformed cells have increased growth, loss of contact inhibition, tumor-specific transplant antigens, and T antigens
• Activated oncogenes

Latent Viral Infection

• Prolonged viral infections, usually fatal, Different from a latent infection in that the infectious virus grows in numbers over time until it is detected. Some persistent viral infections can be caused by conventional viruses.
• Subacute sclerosing panencephalitis (measles virus)

Proteinaceous Infectious particle, Inherited and transmissible by ingestion, transplant, and surgical instruments, Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease, Kuru

• Plant viruses are similar to animal viruses in most respects
• Plant viruses can cause many diseases
• Bean mosaic virus (Beans)
• Wound tumor virus (Corn)
• Potato yellow dwarf virus (potatoes)
• Usually infect plants through damage to cell wall (worms, fungi, insects) and is transferred from plant to plant through pollen.

• Viroids are short pieces of naked RNA with not protein coat
• Nucleotides are often paired, folded, and three-dimentional
• Nucleotide does not code for proteins
• Only a plant pathogen of potatoes