Lecture #2: Bacteria & Viruses Flashcards
what is pathogenesis?
the explanation of how and why a disease develop
what are some components of microbial pathogenesis?
- exposure
- entry
- local replication and spread
- damage to the host
how can microbial pathogenesis cause damage to the host?
- direct damage
- release of toxins and/or irritant enzymes/proteins
- induction of host immune response (innate or adaptive)
what is the mechanism for direct damage by micro-organisms to cell and tissues?
- production of toxins
- production of enzymes
- apoptosis
- virus-induced cytopathic effects: cell lysis
- inclusion bodies: intracytoplasmic or nuclear -transformation
what is the mechanism for damage via the host immune response?
- cytotoxic T cells and natural killer lymphocytes
- autoimmunity
- immediate hypersensitivity (allergy)
- cytotoxic hypersensitivity
- delayed type hypersensitivity
- immune complexes
what are the main causes of disease?
- prions
- virus
- bacteria
- fungi
- protozoa
- toxins
- genetic conditions
- physical agents
- metabolic alterations
what are prions?
- “proteinaceous infectious particle”
- simple proteins smaller than viruses
- lack a genome
- resistant to heat and chemical agents
- form of protein naturally occurring in mammals but their exact purpose remain uncertain (neuronal?)
what is TSE ? when does it occur?
TSE =transmissible spongiform encephalopathy, occurs when non-pathogenic prions are converted into pathogenic forms (resistant to proteases)
pathogenic prions from contaminated food and normal prions interact and transform them into lethal agents
what is the fundamental event in prion disease pathogenesis?
the conformational conversion of the prion protein (PrP) from its normal or cellular form (PrPc) into a disease causing form (PrPsc). Once formed PrPsc replicates by inducing the conversion of PrPc into addational PrPsc molecules
what are some neuropathological features of prion disease?
formation of vacuoles (unstained) and PrP deposits (dark brown)
what are the two types of macromolecules that viruses contain?
nucleic acid and protein (they contain only one species of nucleic acid, either DNA or RNA)
what is an important difference between bacteria and viruses?
bacteria contain both species of nucleic acids (DNA and RNA) whereas viruses contain only one (DNA or RNA not both)
what are some important features of viruses?
- attach to host cell with a specific receptor binding protein
- cannot replicate autonomously (obligate intracellular parasites)
- viruses “hijack” cellular machinery towards the production of new viral particles
what are 5 important structural features of viruses?
- Virion: an individual virus particle
- Nucleocapside: protein coat+ genome
- Capside: a nucleocapsid without a genome
- Capsomeres: protein subunits
- Envelope: viral glycoproteins and a lipid bilayer from host cells
what are some classification criteria for viruses?
- the nucleic acid genome (DNA or RNA)
- the presence or absence of envelope
- the shape of the capsid (icosahedral, helical or complex)
- mode of replication
- cell tropism (preferred cell type for replication)
- type of pathology
what is meant by Icosahedral symmetry? give an example of a virus that has this symmetry.
the capsid consists of 20 triangular facets and 12 corners or apices. ex: Adenovirus
what is meant by helical symmetry?
nucleocapsid proteins are arranged like the steps of a spiral staircase forming long cylinders. Ex: Influenzavirus
what do structural virion proteins do?
- attach to receptors on cells
- protect nucleic acid
- penetrate cell membrane
- replicate nucleic acid (some viruses)
- modify host cell (some viruses)
what do non-structural virion proteins do?
- enzymes needed for DNA replication
- proteins that affect cell physiology
- proteins that suppress the host cell’s defenses
what are the two phases of viral infection and what happens in them?
- the early phase: virus establishes proper cell environment required for viral genome replication and the viral DNA or RNA polymerase is produced
- Late phase: viral genome is amplified and structural components of the virion accumulate. at this point a considerable part of the cellular metabolism is committed to viral reproduction
what is a latent injury?
- reactivation of viral infection at a later time
- transformation and proliferation resulting in neoplasias
what are some determinants of viral tissue tropism?
- host cell receptors for the virus
- cellular transcription factors that recognize viral enhancer and promoter sequences
- anatomic barriers
- local temperature, pH and host defenses
what are some characteristics of bacteria?
- have a single chromosome consisting of circular double stranded DNA coiled in a nucleoid
- have plasmids (DNA that replicate independently of the nucleoid)
- some produce spores in unlivable conditions
why are plasmids important?
important for antibiotic resistance and can encode virulence factors
