2017 Microbiology 1 - Prokaryotic Genetics & Medical Virology Flashcards
What is Reassortment and what types of organisms can participate?
- exchange of genomic nucleic acid segments between strains.
- can take place in some viruses and all eukaryotes
- mechanism by which “genetic shift” takes place
What is Transformation?
Uptake of extracellular DNA by bacteria in a particular physiological state (Competency)
Gram Positive bacteria that can be transformed by exogenous DNA
Streptococcus pneumoniae
S. aureus
Bacillus subtilis
Gram Negative bacteria that can be transformed by exogenous DNA
Neisseria menigitis
Neisseria gonorrhea
Haemophilus influenzae
E. coli
Process of transformation of exogenous DNA into bacteria.
- Transformasome, membrane bound organelles, sequester DNA and transfer it into the cell’s interior
- Degradation of one DNA strand takes place and the other is used in recombination
- DNA recombination may depend on specific donor DNA sequences
What is Conjugation and how does it work?
Fertility plasmid-facilitated transfer of a plasmid or host chromosome to a recipient cell.
Only occurs between strain of the same or closely related species.
Process of Conjugation in Gram-negatives?
- Extrusion of sex pilus from one bacteria
- Pilus adheres to outer membrane of Gram-negative cell walls
- Cells become bound together
- Plasmid undergoes “transfer replication”
- One strand of parental DNA is broken and transferred to the second bacteria
What is an Episome?
A plasmid capable of replicating into the chromosome.
What is the Sex Factors (F factors) and Hfr and their importance?
Sex Factors (Fertility Factors / F) are designated F+ in those that contain it. Those which lack F factors are F- When the F-plasmid is integrated into the chromosome it becomes a Hfr (High Frequency Recombination) donor cell.
F+ transfer plasmid only
Hfr transfer plasmid and some chromosomal genes
Cell properties that can be carried by plasmids:
Drug resistance Toxins Adhesins Growth Factors Production of Antimicrobial agents
What is transduction?
Can occur in Gram+ or Gram - cells when a fragment of DNA is carried to the recipient cell in a virus (Bacteriophage) produced by donor cell.
What are signs of a Viral Infection?
- dsRNA
- Expression of viral protein on surface of plasma membrane, causing activation of Tc cells, NK cells and induction of antibody synthesis
- Formation of inclusion bodies either within cytoplasm or nucleus (very rarely in both)
Cytology of Viral Infections: CPE
Viral inducted cytopathologic effects (CPE)
- inclusion bodies
- cell lysis
- vacuolation
- syncytia (multinucleated cells formed by cell fusion)
Viral Detection via CPE
- inclusions, plaquesor other cytopathological effects may be characteristic of certain viral infections.
- Heterologous interference - the presence of the infection by one virus can prevent the infection of another.
- Hemagglutination Inhibition - certain infections cause the expression of hemagglutinins (receptors) which cause RBCs to bind (hemagglutination).
Viral Detection via Quantization: TCD50, LD50, ID50
Tissue Culture Dose (TCD50) - titer of virus causing CPE in 50% of cultured cells
Lethal Dose (LD50) - titer of virus killing 50% of test animals
Infectious Dose (ID50) - titer of virus infecting 50% of test animals
Plaque forming units - concentration of particules capable of producing a hole in a bacterial lawn or tissue culture monolayer. CPE can also be the end-point in this calculation.
Viral Serology
Virus specific IgM indicates recent infection
Virus specific seroconversion - 4x increase in titer between acute and convalescent phase (~3 wk apart)
Antibody timing - first antibodies at 7-10 days are against host-cell or virion surface antigens (envelope/capsid antigens). Later when cells are lysing, internal antigens are released and induce antibody.
Type 1 Hypersensitivity
IgE fixed to Mast Cells react w/ virus or viral components, triggering the release of Histamine and SRS-A and ECF-A. These acts to cause anaphylactic type reactions (typically localized)
Type 2 Hypersensitivity
IgG/IgM antibodies.
Two types of reactions:
1. Virus (or components) - compliment - antibody complex is fixed to a cell (erythrocyte, leukocyte, platelet), resulting in compliment dependent lysis.Typical of viruses where anemia is one of the clinical manifestations.
2. Viral component (commonly capsid protein) may be expressed on cell. Antibody and compliment bind to infected cell and cause lysis of cell. Thought to be major mechanism of viral-induced cell lysis in tissues.
Type 3 Hypersensitivity
IgG and/or IGM antibodies form complexes w. viral antigens and complement, generally neutrophil chemotactic factors, with resultant local tissue inflammation and destruction.
Type 4 Hypersensitivity
Does not involve antibody.
Sensitized T-lymphocytes react directly with viral antigen, usually that antigen expressed on the surface of infected cell.
Inflammation produced through action of lymphokines and lysing the infected cell.
Second most common hypersensitivity reaction to viruses.
